2. MINERALOGY
Also referred to as mineral science
The study of naturally occurring, crystalline substances –
minerals
Basic to an understanding of the materials largely
responsible for our present technologic culture
3. MINERAL
A naturally occurring homogeneous solid with a definite (but
not necessarily fixed) chemical composition and a highly
ordered atomic arrangement. It is usually formed by
inorganic processes.
naturally occurring – formed by natural processes and not
in the laboratory
*diamond vs. synthetic diamond
*CaCO3 concentric layers in water mains
homogeneous solid – consists of a single solid substance
that can not be physically subdivided into simpler
chemical compounds
*H2O - ice in glaciers
*water
*liquid mercury
mineraloids
4. definite
chemical composition – can be expressed by a
specific chemical formula
*Quartz – SiO2
*Dolomite – CaMg(CO3)2 or Ca(Mg,Fe,Mn)(CO3)2
ordered
atomic arrangement – has an internal structural
framework of atoms or ions arranged in a regular geometric
pattern (crystalline)
*glass – natural solid but amorphous - mineraloid
formed by inorganic processes – includes some organicallyformed compounds
*CaCO3 (aragonite) of mollusk shells
*elemental sulfur – formed by bacterial action
*iron oxide – precipitated by iron bacteria
*mineral fuels - naturally formed but no definite chemical
composition and no ordered atomic arrangement
5. HISTORY OF MINERALOGY
Recent science but the practice of mineralogical arts is as old as
human civilization
Cave paintings of early humans – used natural pigments such as
red hematite (Fe2O3) and black manganese (Mn)
Stone Age – flint tools were prized possessions (paleolithic and
neolithic ages)
Nile Valley – tomb paintings 5000 yrs. ago show busy artificers
weighing malachite and precious metals, smelting mineral ores
and making delicate gems of lapis lazuli and emerald
Bronze Age – other minerals were sought from which metals
could be extracted
384-322 BC Aristotle - theorized that all the known substances
were composed of water, air, earth, and fire and wrote
“Meteorologica”
372-287 BC Greek Philosopher Theophrastus – 1st written work
on minerals “De Mineralibus”
Pliny (400 yrs. later) recorded mineralogical thought of his time
and wrote “Naturalis Historia”
6. HISTORY OF MINERALOGY
1556 Georgius Agricola, German physician, Father of
Mineralogy, published “De Re Metallica” – signaled the
emergence of mineralogy as a science
- Detailed account of mining practices of the time and
includes the first factual account of minerals
1912 US Pres. Herbert Hoover - translated “De Re Metallica”
from Latin to English
1669 Nicholas Steno – important contribution to crystallography through his study of quartz crystals
- Noted that despite differences in origin, size or habit, the
angles between corresponding faces were constant
1780 Carangeot – invented contact goniometer to measure
interfacial crystal angles
1783 Romé de I’Lsle – made angular measurements on
crystals and formulated the law of consistency of interfacial
angle
7. HISTORY OF MINERALOGY
1784 René Haüy – showed that crystals were built by
stacking together tiny identical building blocks which he
called integral molecules
1801 Haüy – developed theory of rational indices for crystal
faces
1809 Wollaston – invented the reflecting goniometer that
permitted highly accurate measurement of the positions of
crystal faces
1779 to 1848 Berzelius – developed the principles of our
present chemical classification of minerals
1815 Cordier – initiated the immersion method which
developed into an important technique for the study of optical
properties of mineral fragments
1828 William Nicol – invented a polarizing device that
permitted the systematic study of the behavior of light in
crystalline substances
8. HISTORY OF MINERALOGY
Late 19th century Federov, Schoenflies and Barlow –
simultaneously developed theories for the internal symmetry
and order within crystals which became the foundations for
X-ray crystallography
1912 Max von Laue – demonstrated that crystal could
diffract X-rays
- Proved that for the first time the regular and ordered
arrangement of atoms in crystalline material
1914 W.H. Bragg and W.L. Bragg – earliest crystal structure
determinations were published
1960s – advent of electron microprobe used in the study of
chemistry of minerals on a microscale
9. ECONOMIC IMPORTANCE OF MINERALS
Before historic time - minerals have played a major role in
man’s way of life and standard of living
Present day – we depend on minerals in countless ways:
Construction
Manufacture of TV sets
Cosmetics
Household cleansers and abrasives
Textile manufacture
Medical purposes
Manufacture of appliances and furniture
Currency and dollar reserves (gold)
Paint pigments
Fertilizer and fertilizer carriers
Machineries
10. NAMING OF MINERALS
MINERAL CLASSIFICATION – based on the presence of
major chemical component (anions or anionic complex)
Native elements
Phosphates
Sulfides
Nitrates
Sulfosalts
Borates
Oxides and Hydroxides
Sulfates
Halides
Tungstates
Carbonates
Silicates, etc
- Requires chemical analysis and measurement of physical
properties such as specific gravity, optical properties and
x-ray parameters
NAMING OF MINERALS – based on some physical property
or chemical aspect, named after a locality, a public figure, a
mineralogist or any other subject considered appropriate
11. NAMING OF MINERALS
Examples of mineral names:
Albite (NaAlSi3O8) from Latin albus (white) in allusion to its
color
Rhodonite (MnSiO3) from Greek rhodon ( a rose) in
allusion to its characteristically pink color
Chromite (FeCr2O4) due to presence of high amounts of
chromium
Magnetite (Fe3O4) due to its magnetic property
Franklinite (ZnFe2O4) after a locality (Franklin, New
Jersey) where it occurs as the dominant zinc mineral
Sillimanite (Al2SiO3) after Professor Benjamin Silliman of
Yale University (1779-1864)
International Mineralogical Association (Commission on New
Minerals and New Mineral Names) reviews all new mineral
descriptions and appropriateness of names
12. NAMING OF MINERALS
As of 2004 there are over 4,000 species of minerals
recognized by the IMA.
150 can be called "common,“
50 are "occasional,“
the rest are "rare" to "extremely rare.“
14. PROPERTIES OF MINERALS
Dependent on:
Chemistry of minerals
chemical composition of minerals
Structure of minerals
geometrical arrangement of the constituent atoms or
ions
nature of electrical forces that bind the atoms
together
15. PHYSICAL PROPERTIES OF MINERALS
Macroscopic expression of the mineral’s internal makeup,
specifically its crystal structure and chemical composition
1.
2.
Crystal shape
1. Crystal form
2. Crystal habit
Properties based on
interaction with light
1. Diaphaneity
2. Luster
3. Streak
4. Play of colors
5. Chatoyancy and
asterism
6. Luminescence
3.
3.
3.
Mechanical properties
1. Cleavage
2. Fracture
3. Parting
4. Hardness
5. Tenacity
Properties related to
mass
1. Density
2. Specific gravity
Other diagnostic
properties
16. PHYSICAL PROPERTIES OF MINERALS
6.
Other diagnostic
properties
1. Magnetism
2. Radioactivity
3. Solubility in acids
4. Sensor properties
5. Electrical properties
17. CRYSTAL SHAPE
a.
a.
Crystal form – the outward appearance of a mineral in a
regular geometric shape
- external form is the outward expression of
the internal ordered atomic arrangement
- examples: garnet – dodecahedron
pyrite – cubic
Crystal habit – general shape of a mineral which also
includes irregularities due to growth
18. CRYSTAL FORMS
If mineral specimens display well-developed crystal forms,
geometric form names are used to describe a mineral’s
outward appearance:
Prismatic – a crystal with one dimension much longer
than the other two
Rhombohedral – having the external form of a
rhombohedron
Cubic – having the external form of a cube
Octahedral – with the external form of an octahedron
19. CRYSTAL HABIT
Crystal habit - typical appearance (shape and size) of
crystals
the many terms used by mineralogists to describe crystal
habits are useful in communicating what specimens of a
particular mineral often look like
helps in identification of minerals
some habits are distinctive of certain minerals, although
most minerals exhibit many differing habits (the
development of a particular habit is determined by the
details of the conditions during the mineral formation/crystal
growth)
warning: crystal habit may mislead the inexperienced as a
mineral's internal crystal system can be hidden or disguised
minerals belonging to the same crystal system do not
necessarily exhibit the same habit
20. CRYSTAL HABITS
Factors that influence the type of Crystal Habits:
a combination of two or more crystal forms
trace impurities present during growth
crystal twinning (occurs when two separate crystals
share some of the same crystal lattice points in a
symmetrical manner)
growth conditions (i.e., heat, pressure, space)
21. HABITS OF CRYSTALS & CRYSTAL AGGREGATES
HABIT
DESCRIPTION
EXAMPLE
Acicular
Needle-like, slender and/or
tapered, from Greek acicula
meaning “root”
Rutile in quartz, sillimanite
Amygdaloidal
Almond-shaped
Heulandite
Anhedral
Poorly formed, external crystal
faces not developed
Olivine
Bladed
Individual crystals are flattened,
blade-like, slender and elongated
Kyanite, stibnite
Botryoidal or
globular
Grape-like, hemispherical masses,
from Greek botrys meaning
“bunch”
Smithsonite,Hemimorphite,
prehnite, chalcedony,
adamite and variscite
Columnar
Stout, column-like individuals
Calcite
Coxcomb
Aggregated flaky or tabular
crystals closely spaced
Barite
Dendritic or
arborescent
Tree-like, branching in one or more
direction from central point, from
dendrron meaning “tree”
Magnesite in opal,
manganese oxides
22. CRYSTAL HABITS
HABIT
DESCRIPTION
EXAMPLE
Dodecahedral
Dodecahedron, 12-sided
Garnet
Drusy or
encrustation
Aggregate of minute crystals
coating a surface
Uvarovite
Enantiomorphic
Mirror-image habit and optical
characteristics; right- and lefthanded crystals
Quartz
Equant, stout,
stubby or blocky
Length, width, and breadth roughly
equal
Zircon
Euhedral
Well-formed, external crystal faces
developed
Spinel
Fibrous or
columnar
Extremely slender prisms that are
flexible thread-like grains or fibers
Tremolite, chrysotile
Filiform or
capillary
Hair-like or thread-like, extremely
fine
Natrolite
Foliated or
micaceous
Layered structure, parting into thin
sheets easily
Mica
23. CRYSTAL HABITS
HABIT
DESCRIPTION
EXAMPLE
Granular
Aggregates of anhedral crystals 210 mm. in matrix
Scheelite
Hemimorphic
Doubly terminated crystal with two
differently shaped ends
Hemimorphite
Mamillary
Breast-like: surface formed by
intersecting partial spherical
shapes
Malachite
Massive or
compact
Shapeless, no distinctive external
crystal shape, very fine grained
Serpentine, goethite
Nodular or
tuberose
Deposit of roughly spherical form
with irregular protuberances
Geodes
Octahedral
Octahedron, eight-sided (two
pyramids base to base)
Diamond
Plumose
Fine, feather-like scales
Mottramite
Prismatic
Elongate, prism-like: crystal faces
parallel to c-axis well-developed
Tourmaline
24. CRYSTAL HABITS
HABIT
DESCRIPTION
EXAMPLE
Pseudohexagonal
hexagonal appearance due to
cyclic twinning
Aragonite
Pseudomorphous
Occurring in the shape of another
mineral through pseudomorphous
replacement
Tiger's eye
Radiating or
divergent
Acicular crystals radiating outward
from a central point
Pyrite suns, wavellite,
goethite
Reniform or
colloform
Similar to mamillary: intersecting
kidney-shaped masses
Hematite
Reticulated
Acicular crystals forming net-like
intergrowths
Cerussite
Rosette
Platy, radiating rose-like aggregate
Gypsum
Sphenoid
Wedge-shaped
Sphene
Stalactitic
Forming as stalactites or
stalagmites: cylindrical or coneshaped
Rhodochrosite
25. CRYSTAL HABITS
HABIT
DESCRIPTION
EXAMPLE
Stellate
Star-like, radiating
Pyrophyllite
Striated/striations
Surface growth lines parallel or
perpendicular to a crystallographic
axis
Chrysoberyl
Subhedral
External crystal faces only partially
developed
Tabular
Flat, tablet-shaped, prominent
pinnacoid
Ruby
Wheat sheaf
Aggregates resembling handreaped wheat sheaves
Zeolites
Lamellar
Made up of layers, like the leaves
in a book
Graphite, molybdenite
Banded
Single mineral may show a thin
and roughly parallel banding, or 2
or more minerals form a finely
banded intergrowth
Banded malachite, chert
and hematite intergrowth
26. CRYSTAL HABITS
HABIT
DESCRIPTION
EXAMPLE
Concentric
Bands or layers are arranged
concentrically about one or more
centers
Agate
Geode
A rock cavity lined with mineral
matter but not completely filled.
Maybe banded as in agates,
containing a central portion filled
with euhedral crystals projecting
into an open space
Oolitic
Made up of oolites, which are
small, round or ovate accretionary
bodies and resemble the roe of
fish
Oolitic iron ore
Pisolitic
Made up of pea-sized grains,
similar to oolitic but coarser
Bauxite
27. CRYSTAL HABIT
Qualities of Crystal Development:
Euhedral – a mineral that is completely bounded
by crystal faces (well-formed); from the Greek eu
which means “good” and “hedron” meaning “plane”
Subhedral – a mineral grain that is partly bounded
by crystal faces and partly by irregular surfaces;
from the Greek sub which means “less than”
Anhedral – a mineral that lacks crystal faces and
that may show rounded or irregular surfaces; from
the Greek an meaning “without”
The qualities are a reflection of the space that was
available to the crystal at the time of its growth
28. DIAPHANEITY
a
measure of the amount of light that can be
transmitted by a mineral (light-transmitting qualities)
From the Greek work diaphanes meaning “transparent”
Transparent – transmits light allowing objects to
be seen through it (ulexite, gemstones)
Transluscent – capable of transmitting light
diffusely but it is not ransparent. It does not show
a sharp outline of an object seen through it.
Opaque – impervious to visible ligh, even on thin
edges of the mineral
29. LUSTER
Luster – refers to the general appearance of a mineral
surface in reflected light
Types of Luster:
Metallic – characterized by a brilliant appearance of a
metal
̶ Opaque to light
̶ Has black or very dark streak
Sub-metallic – intermediate between metallic and non
metallic.
̶ Similar luster to metal, but are duller and less
reflective
̶ Often occurs in near-opaque minerals with very
high refractive indices, such as sphalerite,
cinnabar and cuprite
Non-metallic – generally light colored and transmits light
̶ colorless to very light colored
30. LUSTER
TYPE OF NONMETALLIC
LUSTER
DESCRIPTION
Vitreous
Luster of polished glass. One of the
most common luster and occurs in
transparent or translucent minerals with
relatively low refractive indices (eg.
calcite, quartz and fluorite)
Resinous
Has the appearance of resin, chewing
gum or smooth-surfaced plastic (eg.
amber – a form of fossilized resin,
sphalerite and sulfur)
Greasy
Resembles fat or grease or with a layer
of oil. Often occurs in minerals containing a great abun-dance of microscopic
inclusions. Many minerals with a greasy
lustre also feel greasy (eg. opal and
cordierite)
31. LUSTER
TYPE OF NONMETALLIC
LUSTER
DESCRIPTION
Pearly
Iridescent pearl-like luster in minerals
consisting of thin transparent co-planar
sheets. Light reflecting from these
layers give them a luster reminiscent of
pearls. Such minerals possess perfect
cleavage (muscovite mica and stilbite)
Silky
Silk-like. Caused by the reflection of
light from a fine fibrous parallel aggregate (asbestos, ulexite, satin spar,
chrysotile and malachite)
Adamantine
A hard, brilliant luster. Superlative lustre
seen in transparent or translucent
having a high refractive index, from
Greek adamos meaning “shine” (eg.
Cerussite,diamond, garnet and zircon)
32. LUSTER
TYPE OF NONMETALLIC
LUSTER
DESCRIPTION
Dull or earthy
Exhibits little to no luster, due to coarse
granulations which scatter light in all
directions, approximating a Lambertian
reflector. A distinction is sometimes
drawn between dull minerals and
earthy minerals, with the latter being
coarser, and having even less lustre
(eg. Kaolinite, goethite, limonite)
Waxy
A luster resembling appearance of wax
(eg. jade and chalcedony)
33. STREAK
Streak
– color of a finely powdered mineral
̶ usually constant and thus, useful in mineral
identification
̶ determined by rubbing the mineral on a
piece of unglazed porcelain or streak plate
̶ if no streak seems to be made, the mineral's
streak is said to be white or colorless
̶ streak is particularly important as a
diagnostic for opaque and colored materials
̶ less useful for silicate minerals, most of
which have a white streak and are too hard
to powder easily. The streak plate has a
hardness of a bout 7 and thus, it cannot be
used with minerals with greater hardness
34. STREAK
Streak
̶
̶
̶
̶
̶
̶
̶
̶
Examples:
Cinnabar (dark red color) dark red streak
Azurite (blue color) blue streak
Fluorite (green, purple or yellow color)
white streak,
Hematite (black color) red streak
Galena (black color) gray streak
Pyrite (brass or gold yellow) green streak
Sphalerite (dark brownish black to honey
rown) pale yellow streak
35. COLOR
Color – directly related to the chemistry and structure of
mineral. When the chemical element causing the color is
essential to a mineral, color can be used as a diagnostic
tool because such a mineral has a constant color
Sulfur – yellow
Malachite – green
Turquiose – greenish blue to blue-green
most minerals with a metallic luster vary little in color
and the color of freshly broken surface of a metallic
mineral is diagnostic
Galena – bright bluish lead gray color becomes dull
gray
Bornite – brownish-bronze color when fresh and
tarnish to iridescent metallic purples and blues
(peacock ore)
36. COLOR
Color – results in minerals when certain wavelengths of light
are absorbed. Color results from the combination of those
wavelengths that reach the eye
When light strikes the surface of a mineral, part of it is
reflected and part refracted. If light suffers no absorption, the
mineral is colorless
Pleochroism – selective absorption of light by minerals
resulting in a display of different colors when light is
transmitted along different crystallographic directions (eg.
Cordierite)
37. COLOR, STREAK AND OPTICAL PHENOMENA
Dichroism – selective absorption of light along two
crystallographic directions resulting in a display of
different colors (eg. tourmaline)
Idiochromatic minerals – minerals where color
serves as an important means of identification
Malachite – green
Azurite – blue
Rhodonite and rhodochrosite – rose red or rose
pink
Chalcopyrite – brass yellow
Niccolite – copper red
Bornite – peacock ore
Allochromatic minerals – minerals that produce no
characteristic colors and colors vary depending on
the presence of impurities like Fe
38. COLOR, STREAK AND OPTICAL PHENOMENA
Play of Colors
the striking play of colors in minerals that result from
the interference of light as the angle of incident light
changes either at the surface or in the interior of a
mineral
Caused by the diffraction of light from closely spaced
features such as packed spheres (opal) or fine
lamellae within the mineral (plagioclase), closely
spaced fractures, cleavage planes or exsolution
lamellae
eg. Precious opal – interference of light reflected from
sub-microscopic layers of nearly spherical particles
arranged in a regular pattern
39. COLOR, STREAK AND OPTICAL PHENOMENA
Play of Colors
Opalescence – pearly color produced by scattering of
light in common opal due to absence of microscopic
layering
Iridescence – caused by light defracted and reflected
from closely spaced fractures or cleavage planes in
parallel orientation or thin surface films (internal and
surface) – bornite, hematite, limonite and sphalerite
Schiller - colorful iridescence that occurs when light is
reflected between layers (eg. moonstone and
labradorite), also called labradorescence
40. OTHER OPTICAL PHENOMENA
Chatoyancy
the silky appearance which results from closely
packed parallel fibers
a display of luminous bands, which appear to move
as the specimen is rotated. Such minerals are
composed of parallel fibers (or contain fibrous
voids or inclusions), which reflect light into a
direction perpendicular to their orientation, thus
forming narrow bands of light
Examples:
Cat's eye
(chrysoberyl)
Cymophane
Tiger’s eye
(qtz w/ amphibole)
41. OTHER OPTICAL PHENOMENA
Asterism
the display of a star-shaped luminous area
triple chatoyancy
Examples:
Some sapphires and rubies
Aventurescence
is a reflectance effect like that of glitter
It arises from minute, preferentially oriented mineral
platelets within the material. These platelets are so
numerous that they also influence the material's body
color
Examples:
aventurine quartz
42. LUMINESCENCE
Luminescence – emission of light by a mineral that is not a direct
result of incandescence
Occurs in minerals containing foreign ions or “activators”
Usually faint and can be seen only in the dark
Types of Luminescence:
Fluorescence – luminescence that occurs during exposure of a
mineral to ultraviolet light, x-rays or cathode rays
Produced when the energy of shortwave radiation is absorbed
by impurity ions and released as longer wave radiation
Color of emitted light varies considerably with wavelengths or
source of ultraviolet light
eg. Fluorite (blue fluorescence due to organic materials or rare
earth ions), scheelite (pale blue fluorescence due to Mo
replacing W), willemite, calcite, diamond, hyalite, scapolite,
eucryptite (salmon pink)
Synthetic phospors : fluorescent lamps, paints, cloth and tapes
43. LUMINESCENCE
Phosphorescence
– luminescence that continues after the
exciting rays are cut off
Thermoluminescence – visible light emitted by some
minerals when heated to a temperature below that of red
heat
Best shown by non metallic minerals that contain
foreign ions as activators
eg. Fluorite, chlorophane calcite, apatite, feldspar
Triboluminescence – luminosity of some minerals after
having been crushed, scratched or rubbed
Mostly occurs in non metallic minerals that possess
good cleavage
eg. Fluorite, sphalerite, lepidolite
44. CLEAVAGE, PARTING AND FRACTURE
Cleavage - tendency of crystalline materials to split along
definite crystallographic structural planes (parallel to atomic
planes) creating smooth surfaces
Parallel to crystal faces
Result from:
Weak type of bond
Greater spacing between the planes
Combination of the 2
Cleavage quality
Perfect
Good
Fair
obscure
absent
45. CLEAVAGE, PARTING AND FRACTURE
Types of Cleavage:
Basal or pinacoidal cleavage - occurs parallel to the base
of a crystal, the {0001} crystal plane (eg. mica group,
graphite)
Cubic cleavage - occurs on the {001} plane parallel to the
faces of a cube. This is the source of the cubic shape
seen in crystals (eg. ground table salt, halite and galena)
Octahedral cleavage - occurs on the {111} crystal plane
forming octahedra shapes. Common semiconductors. (eg.
diamond and fluorite)
Dodecahedral cleavage - occurs on the {011} crystal
planes forming dodecahedra.(eg. wulfenite and gypsum)
Rhombohedral cleavage - occurs parallel to the {1011}
faces of a rhombohedron. (eg. Calcite and other
carbonate minerals)
Prismatic cleavage - parallel to a vertical prism {110}. (eg.
cerussite, tremolite and spodumene)
50. CLEAVAGE, PARTING AND FRACTURE
Parting – tendency for a mineral to break along planes of
structural weakness due to external stress or along twin
composition planes
Result from:
Pressure
Twinning
Parting breaks are very similar in appearance to cleavage
Types of Parting:
octahedral parting (eg. Magnetite)
rhombohedral parting (eg. Corundum)
basal parting (eg. Pyroxenes)
51. CLEAVAGE, PARTING AND FRACTURE
Uses/Importance of Cleavage and Parting:
traditional physical property used in mineral identification
both in hand specimen and microscopic examination of
rock and mineral studies
technical importance in the electronics industry and in the
cutting of gemstones
Precious stones are generally cleaved by impact as in
diamond cutting
52. CLEAVAGE, PARTING AND FRACTURE
Fracture – the way a mineral breaks when it does not yield
along cleavage or parting surfaces
Types of Fracture:
Conchoidal fracture – smooth, curved fracture resembling
the interior surface of a shell
Fibrous or splintery fracture –
Hackly fracture – jagged fractures with sharp edges
Uneven or irregular fracture – fractures producing rough
and irregular surfaces
53. HARDNESS
Hardness – or “scratchability” is the resistance that a
smooth surface of a mineral offers to scratching
Designated by (H)
Dependent on type of bonding and crystal structure
Determined by observing comparative ease or
difficulty with which one mineral is scratched by
another mineral or by a file or a knife
Uses a scale of 10 Minerals (Mohs Scale)
Mohs Scale of Hardness – introduced by F. Mohs in
1824
arranged in an order of increasing relative hardness
purely ordinal scale (eg. corundum (9) is twice as
hard as topaz (8), but diamond (10) is almost four
times as hard as corundum)
Absolute hardness – measured using a sclerometer
54. HARDNESS
There is a link between hardness and chemical
composition
Most hydrous minerals are relatively soft (H <5)
Halides, carbonates, sulfates and phosphates are
relatively soft (H <5.5)
Most sulfides are relatively soft (H <5) with pyrite
being and exception (H ~6 to 6.5)
Most anhydrous oxides and silicates are hard (H
>5.5)
56. HARDNESS
On the Mohs Scale:
pencil lead - 1
fingernail - 2.5
copper penny - 3.5
knife blade - 5.5
window glass - 5.5
steel file - 6.5
Using these ordinary materials of known hardness can
be a simple way to approximate the position of a
mineral on the scale.
58. HARDNESS
Intermediate Hardness
Hardness
1
2.5 to
3
Substance or Mineral
Talc
pure gold, silver, aluminum
3
Calcite, copper penny
4
Fluorite
4 to
4.5
Platinum
4 to 5
Iron
Hardness
Substance or Mineral
7
Quartz
7 to
7.5
Garnet
7 to 8
8
8.5
9
Hardened steel
Topaz
Chrysoberyl
Corundum
5
Apatite
9 to
9.5
6
Orthoclase
<10
Ultrahard fullerite
6
Titanium
10
Diamond
6.5
Iron pyrite
>10
Aggregated diamond
nanorods, Rhenium diboride
6 to 7
Glass, Vitreous pure silica
Carborundum
59. TENACITY
Tenacity- the resistance that a mineral offers to
breaking, bending, or tearing
“cohesiveness” of a mineral
Types:
Brittleness – ability to break or powder easily (halite)
Malleability – the ability to be hammered out into thin
sheets (copper)
Sectility – the ability to be cut into thin shavings with
a knife (chalcocite)
Ductility – ability to be drawn into wires (gold)
Flexibility – can be bent but does not resume original
shape when pressure is released (chlorite, talc)
Elasticity – can be bent and return to original shape
upon release of pressure (mica)
60. DENSITY AND SPECIFIC GRAVITY
Density – defined as mass per unit volume
ρ m
=
v
Specific gravity – or “relative density”
Designated by (G)
A number that expresses the ratio between the
weight of a substance and the weight of an equal
volume of water at 4°C
eg. a mineral with a specific gravity of 2 weighs twice
as much as the same volume of water
Useful in fine crystal or gemstones when other test
could injure the specimen
Dependent on:
kind of atoms of which it is composed (eg. Olivine
– solid solution series between fosterite Mg2SiO4
with G 3.3 and fayalite Fe2SiO4 with G 4.4)
61. SPECIFIC GRAVITY
Manner
in which the atoms are packed together
(eg. Diamond – closely packed →3.5 vs. graphite
– C atoms loosely packed →2.23)
Average specific gravity for non metallic minerals → G
2.65 to G 2.75 → this is because the specific gravities
of the most common non metallic minerals quartz is
2.65, feldspar is 2.6 to 2.75 and calcite is 2.72
ulexite G 1.96 – light, barite G 4.5 – heavy
Average specific gravity for metallic minerals → G 5.0
→ this is because the specific gravities of the most
common metallic mineral pyrite is 5.0
Graphite G 2.23 – light, silver G 10.5 - heavy
62. DETERMINATION OF SPECIFIC GRAVITY
For accurate determination of specific gravity, the
mineral specimen must be:
homogeneous and pure
compact with no cavities or cracks within which
bubbles or films of air could be imprisoned
Modes of Specific Gravity Determination:
Jolly balance
Pycnometer
63. DETERMINATION OF SPECIFIC GRAVITY:
Weigh the mineral in air (Wa).
Immerse in water and weigh again → (Ww). (under these
conditions it weighs less, since in water it is buoyed up by a
force equivalent to the weight of the displaced water)
(Wa – Ww) is equal to the apparent loss of weight or equals the
weight of an equal volume of water
Specific Gravity (G) =
Wa
-----------------
Wa – Ww
64. DETERMINATION OF SPECIFIC GRAVITY
BY JOLLY BALANCE:
Place a fragment on the upper scale pan and record the
elongation of the spring. This is proportional to the weight in
air Wa
Transfer the fragment into the lower pan and immersed in
water
Record the elongation of the spring. This is proportional to
the weight of the fragment in water Ww
Note:
*torsion balance used for obtaining specific
gravities of small particles weighing less than 25 mg.
*because specific gravity is merely a ratio, it is not
necessary to determine the absolute weight of the
specimen but mere values proportional to the weights in
air and water
65. DETERMINATION OF SPECIFIC GRAVITY
BY PYCNOMETER:
Dry pycnometer bottle is weighed (P).
Mineral fragments are then introduced into the bottle and a
second weighing (M) is made
(M – P) represents the weight of the sample in air
The bottle containing the mineral sample is partially filled
with distilled water and boiled for a few minutes to drive off
any air bubbles
After cooling, the pycnometer is further filled with distilled
water and weighed (S), care being taken that the water rises
to the top of the capillary opening but that no excess water is
present
The last weighing is made (W) is made after emptying the
bottle and refilling with distilled water alone
66. DETERMINATION OF SPECIFIC GRAVITY
BY PYCNOMETER:
In the last step, the pycnometer contains more water than in
the previous weighing; the volume of water added is equal to
the aggregate volume of the grains comprising the sample
The specific gravity is determined:
G = (M – P)
------------W + (M – P) - S
Where: M – P = weight of sample
W = pycnometer + water content
S = sample + pycnometer + undisplaced water
W + (M – P) – S = weight of water displaced by sample
Method used when a mineral can not be obtained in a
homogeneous mass large enough to permit use of the
balance method
67. ELECTRICAL PROPERTIES
Conduction of electricity in crystals is related to the type
of bonding
Pure metallic bonding – excellent conductors
Partially metallic – semi-conductors (some sulfide
minerals)
Ionic or covalent bonding – non conductors
Electrical conductivity for non isometric minerals –
vectorial property varying with crystallographic direction
(eg. Graphite better conductor at right angles to the caxis than parallel to it)
68. ELECTRICAL PROPERTIES
PIEZOELECTRICITY
occurs in crystals with polar axis (polar axis is present in crystals that lack a center of symmetry – 21 of
the 32 crystal classes have no center of symmetry)
A flow of electrons toward one end producing
negative electrical charge while a positive charge is
induced at the opposite end if pressure is exerted at
the ends of the polar axis
First detected in quartz in 1881 by Pierre and
Jacques Curie
Practical uses:
sound waves produce by submarines could be detected by the piezoelectric current generated when
they impinge on a submerged quartz
69. ELECTRICAL PROPERTIES
PIEZOELECTRICITY
Practical uses:
Piezoelectric property of quartz was first used in
1921 to control radio frequencies. When subjected
to an alternating current, a properly cut slice of
quartz is mechanically deformed and vibrates by
being flexed first one way and then the other, the
thinner the slice, the greater the frequency of
vibration. By placing a quartz plate in the electric
field generated by a radio circuit, the frequency of
transmission or reception is controlled when the
frequency of the quartz coincides with the
oscillations of the circuit
70. ELECTRICAL PROPERTIES
PIEZOELECTRICITY
Practical uses:
Tiny quartz plate used in digital quartz watches
serves the same function as quartz oscillators
used to control radio frequencies. It mechanically
vibrates at a constant predetermined frequency
controlling accurately the radio frequency of the
electronic circuit in the watch
71. ELECTRICAL PROPERTIES
PYROELECTRICITY
Observed in crystals with polar axes (primary
pyroelectricity is shown in crystals that belong to 10
crystal classes having a unique axis – eg.
tourmaline)
Simultaneous development of positive and negative
charges at opposite ends of a polar axis due to
temperature changes
72. MAGNETIC PROPERTIES
MAGNETISM
Being attracted to a magnet
Use to separate minerals by magnetic separator
Types:
a. Ferromagnetic
• Being attracted to a small hand magnet (ie.
magnetite Fe3O4 and pyrrhotite Fe-xS
a.
a.
Paramagnetic
• Minerals containing iron being attracted in a field
of powerful electromagnet
Diamagnetic
• Minerals repelled in a field of powerful
electromagnet
73. RADIOACTIVITY
Minerals containing radioactive elements like uranium
and thorium will continually undergo decay reactions in
which radioactive isotopes of U and Th for various
daughter elements
During decay they release energy in the form of alpha
and beta particles and gamma radiation
Examples of radioactive minerals: uraninite,
pitchblende, thorianite and autunite
74. SOLUBLITY IN ACID
Some minerals undergo visible reaction with dilute
hydrochloric acid
CaCO3 + 2 H → Ca
2+
+ CO2 ( gas ) + H 2O
As the calcite dissolves, it releases carbon dioxide gas
hat bubbles in the liquid, producing the familiar “fizz”
Calcite, aragonite, witherite, and strontianite as well as
Cu-carbonates, show bubbling or effervescence when a
drop of dilute HCl is placed on the mineral
Other carbonates like, rhodochrosite, dolomite,
magnesite and siderite show effervescence only in hot
HCl
75. SENSORY PROPERTIES
Odor
– sulfur smells like the gas produced by rotten
egg, Clay smell earthy
Taste – halite taste salty, sylvite tastes salty and
bitter
Feel – greasy feel for molybdenite, graphite and talc
77. ATOMS AND IONS- THE BUILDING BLOCKS
Matter is made up of atoms.
The structure of atoms dictate their properties. How
atoms combine dictate what we see in the many
minerals in nature.
New
technologies allow us to peer ever closer at the
minute structures of minerals, down to the scale of
individual atoms
78. ATOMS AND IONS – THE BUILDINGBLOCKS
Atom is smallest subdivision of matter that retain the
characteristics of the elements. Although one can subdivide atoms into numerous subatomic particles, we will
be concerned only with protons, neutrons and
electrons.
Protons and neutrons are together in the nucleus of an
atom, whereas electrons are in motion in orbits around
the central nucleus. Protons carry a positive electrical
charge, electrons carry a negative charge, and neutrons
carry no charge. Neutrons work to keep nuclei together.
Most atoms are electrically neutral, meaning that they
have an equal number of protons and electrons
79. ATOMS AND IONS – THE BUILDING BLOCKS
Very small massive nucleus composed of protons and
neutrons surrounded by a much larger region populated
by electrons, except in Hydrogen
Not visible to naked eye and even with highest
magnification of the electron microscope
Sizes are measured as atomic radius in Å (0.46 to 2.62
Å)
Each electron moves in an orbit around the nucleus and
carries negative electricity. Distance from nucleus
depends on the energies of the electrons
Electrons and nuclei are both extremely small but the
electrons move very rapidly around the nuclei → give
large effective diameters (10k-20k times)
80. ATOMS AND IONS
A schematic model of a lithium (Li) atom in the ground
state. It has 3 protons in the nucleus, and 3 electrons in
orbit. (we will get to the number of neutrons)
81. ELECTRONIC AND NUCLEAR PROPERTIES
Properties of atoms reflect some combination of features related to electrons or to the nucleus.
The electronic properties are those related to how
atoms connect to one another: bonding.
.
The nuclear properties include features like radioact-
ivity
82. SIZE OF NUCLEI
The number of neutrons tends to closely follow the number of protons. Atoms
with more of each are bigger and heavier.
A uranium atom, with 92 protons
and ~146 neutrons is gigantic
compared to dinky helium (2 + 2).
83. THE SPACIOUS ATOM
Microcosms of our solar system, atoms are dominantly empty space:
electron orbits
If an oxygen atom had a
total radius of 100 km,
the nucleus would be a
~1 m diameter sphere in
the middle.
84. ELECTRONS IN ORBIT
In a simplistic model, electrons float around the nucleus in orbits that
are sometimes called shells.
electron orbits
As the number of
electrons increases, they
start to fill orbits farther out
from the nucleus.
In most cases, electrons
are lost or gained only
from the outermost orbits.
85. CHARGED ATOMS: IONS
Left to their own devices, atoms are electrically neutral.
That means that they have an equal number of protons
and electrons.
During the course of most natural events, protons are
not gained or lost, but electrons may be.
Atoms with more or fewer electrons than protons are
electrically charged. They are called ions: an atom
that loses electrons takes on a positive charge (cation);
an atom that gains electrons takes on a negative
charge (anion).
86. ATOMIC NUMBER
We distinguish one element from another on the basis
of the atomic number, which is the number of protons.
So, an atom of any element can have a variable number of electrons and neutrons, but given the number of
protons, the fundamental properties of the element are
unchanged. This is the basis for Dmitri Mendeleev’s
organization of the Periodic Table of the Elements. The
table is a way of organizing elements on physical
grounds, but also serves to group elements with
consistent chemical properties.
87. THE PERIODIC TABLE
The
periodic table is read from top to bottom, left to
right, as atomic number increases: 1=H, 2=He,
3=Li, 4=Be, 5=B, 6=C, and so on.
88. THE PERIODIC TABLE
alkali
earths
Elements in columns (groups) have similar outer-electron
configurations, and so tend to behave similarly.
transition metals
alkalis
halogens
rare
earths
noble gases
actinides
89. OXIDATION STATE
Most atoms will form the same kinds of ions all the time. For example, all the alkalis form +1 ions, and the halogens form -1 ions.
alkalis
halogens
90. OXIDIZED AND REDUCED STATES
transition metals
The transition metals are more electronically complex. They may
form ions of various charges. For example, iron (Fe) is found as +2
and +3 ions.
A transition metal cation with a higher charge is more oxidized than
one of lower charge. That comes from the fact that materials with high
proportions of Fe+3/Fe+2 form in environments where oxygen is
abundant. The opposite is also true, and we call Fe+2 reduced iron.
91. THE PERIODIC TABLE: THE BULK EARTH
A small number of elements make up >99% of the solid Earth.
O = oxygen
Na = sodium
Mg = magnesium
Al = aluminum
Si = silicon
S = sulfur
Ca = calcium
Fe = iron
Ni = nickel
92. THE PERIODIC TABLE: THE CRUST
The crust is a little more elementally interesting (again, as a result of
differentiation), but it is still mainly made of a small number of
elements.
C = carbon
P = phosphorus
K = potassium
Ti = titanium
Mn = manganese
93. ATOMIC WEIGHT: IT’S ALL IN THE NUCLEUS
Since electrons weigh virtually nothing, the mass of an atom is concentrated in
its nucleus.
Each atom can be described by its atomic weight (or mass),
which is the sum of the protons and neutrons.
lithium:
atomic number = 3
3 protons
4 neutrons
atomic weight = 3 + 4 = 7
BUT... although each element has a
defined number of protons,
the number of neutrons is not fixed.
Atoms with the same atomic number but
variable numbers of neutrons are called
isotopes.
94. STABLE AND RADIOACTIVE ISOTOPES
Carbon (atomic # 6) has three natural isotopes
with atomic weights of 12, 13 and 14.
isotope #p
#n
========
==
C-12
6
6
C-13
6
7
C-14
6
8
C-14 is a radioactive isotope; C-12 and C-13 are stable.
Over time the proportion of C-12/C-14 and C-13/C-14
will increase until there is no C-14.
(unless some process makes new C-14...)
95. ATOMS AND IONS
Atomic particles can exist only with certain energy
configurations (Max Planck) → basis of Quantum Theory
Quantum Theory – energy exists on an atomic scale only as
discrete bundles and not as an infinitely divisible spectrum
Thus, electrons surrounding the nucleus can occupy only
specific energy levels which differ by discrete number of
quanta
Atomic number – the positive charge is the same as the
number of protons, and this number, equal to the number of
electrons is called the atomic number Z
Characteristic mass or mass number – determined by the
sum of protons and neutrons
Isotopes – atoms of the same element but with differing
numbers of neutrons (eg. O with Z=8 : O16, O17 and O18)
96. ATOMS AND IONS
Atomic weight – number expressing relative weight of an
element in terms of the weight of the element oxygen
Characteristics of an element depend on the configuration of
the electronic structure of its atoms
97. RADIOACTIVITY INSIDE YOU
Concerned about radioactivity in nature?
To keep things in perspective, consider that 0.01% of all potassium is
radioactive K-40.
Potassium is an essential element in the human body.
If your body is about 1% K, this means a 70 kg
(150 pound) person contains around
1x1021 atoms (that’s one billion trillion atoms)
of radioactive K-40.
98. BONDING FORCES IN CRYSTALS
Forces that bind atoms or ions of crystalline solids together
are electrical in nature
Type and intensity of bond are responsible for physical and
chemical properties of minerals (hardness, cleavage,
fusibility, electrical and thermal conductivity and coefficient of
thermal expansion)
The stronger the bond → harder crystal
→ higher melting point
→ smaller thermal expansion coeff.
Diamond (C) – hardness due to very strong electrical
forces linking carbon atoms
Periclase (MgO) and halite (NaCl) – have similar structural
patterns but halite melts at 801 °C while periclase at 2800
°C due to stronger electrical bond requiring larger heat
energy to separate atoms
99. BONDING FORCES IN CRYSTALS
One
typical consequence of chemical reactions is
the formation of chemical bonds between atoms and
complexes. What kind of bonds form is based on the
electronic configuration of the atoms involved.
Atoms with near-full (halogens) and near-empty
(alkalis/alkali earths) outer electron shells, as well as
transition metals, may form ionic bonds.
Covalent bonds are where atoms share outer shell
electrons.
The bulk of minerals are dominantly ionically
bonded. However, many minerals have bonds with
some covalent and some ionic components.
100. BONDING FORCES IN CRYSTALS
Types of Chemical Bonds:
Ionic bond (moderate hardness and SG, high melting
and boiling points, poor conductors of heat and
electricity)
Covalent bond – strongest chemical bond (very high
melting and boiling points, great stability)
Metallic bond (high plasticity, tenacity, ductility and
conductivity, low hardness, low melting and boiling
points)
Van der Waals’ bond (weak)
101. ATOMIC STRUCTURE
• Protons and neutrons form the nucleus of
an atom
– Represents tiny fraction of the volume at
the center of an atom, but nearly all of
the mass
• Electrons orbit the nucleus in discrete shells
or energy levels
– Shells represent nearly all of the volume
of an atom, but only a tiny fraction of the
mass
– Numbers of electrons and protons are
equal in a neutral atom
– Ordinary chemical reactions involve only
outermost shell (valence) electrons
103. CHEMICAL BONDING
• Chemical bonding is controlled by
outermost shell (valence)
electrons
• Elements will typically be reactive
unless their valence shell is full
• Atoms or groups of atoms with
unequal numbers of protons and
electrons, thus having a non-zero
charge, are called ions. Positively
charged ions are known as
cations, and negative charges as
anions.
• Positive and negative ions are
attracted to one another and may
stick or chemically bond together
104. IONIC BONDS
Atoms satisfy themselves
by the give and take of
outer shell electrons.
Most minerals are held
together by primarily ionic
bonds.
105. COVALENT BONDS: ELECTRON SHARING
These carbon atoms are held together by sharing outer-shell
electrons.
106. BONDING FORCES IN CRYSTALS
PROPERTY
IONIC BOND
COVALENT BOND
METALLIC BOND
VAN DER WAAL’S BOND
BOND STRENGTH
Strong
Very strong
Variable strength but
generally moderate
Weak
MECHANICAL
Moderate to high hardness
depending on interionic
distance; brittle
Great hardness; brittle
Low to moderate hardness;
gliding common; high
plasticity; sectile; ductile;
malleable
Crystal soft and somewhat
plastic
ELECTRICAL
Poor conductors in solid
state, melts and solutions
conduct by ion transport
Insulators in solid state
Good conductors; conduction
by electron transport
Insulators in both solid and
liquid state
THERMAL (melting
point, coefficient of
thermal expansion)
Moderate to high MP
depending on interionic
distance; low coefficient of
thermal expansion
High MP, low coefficient of
thermal expansion
Variable MP and coefficient
of thermal expansion
Low MP, high coefficient
of thermal expansion
SOLUBILITY
Soluble in polar solvents
Very low solubilities
Insoluble except in acids or
alkalis by chemical reaction
Soluble in organic solvents
to yield solutions
STRUCTURAL
Non-directed; gives structure
of high coordination and
symmetry
Highly directional; gives
structures of lower
coordination and symmetry
Non-directed; gives
structures of very high
coordination and symmetry
Non-directed; symmetry
low because of shape of
molecules
EXAMPLES
Halite (NaCl)
Calcite (CaCO3)
Fluorite (CaF2)
Diamond (C)
Sphalerite (ZnS)
O2 molecules
Graphite C)
Organic molecules
Copper (Cu)
Silver (Ag)
Gold (Au)
Most metals
Iodine (I2)
Organic compounds
Most minerals
107. CHEMICAL REACTIONS: ACHIEVING
STABILITY
Chemical
reactions take place in order to achieve a
more stable state (lower total energy) under given
conditions (pressure, temperature).
Unstable reactants react to form stable products
To complicate this, the transition from unstable
mineral to stable mineral is not necessarily automatic. Many chemical reactions require great deal of
energy to run to completion
108. STABILITY AND METASTABILITY
Minerals that persist in an environment in which they are
not chemically stable are said to be metastable.
Most of the minerals in the rocks at the Earth’s surface are
metastable. Given enough energy (or enough time and the
p re s s u re
right conditions) they will react to form stable minerals.
d ia m o n d s t a b le
g r a p h ite s ta b le
Earth’s surface
conditions
te m p e ra tu re
109. CHEMICAL COMPOSITION OF MINERALS
Most minerals have compositions corresponding to chemical compounds.
But a few occurs as elements (native) such as native gold, native copper
and native sulfur
Minerals are seldom chemically pure (except quartz and kyanite), and
compositions seldom correspond to an ideal chemical formula →
“characteristic chemical composition”
Chemical formulas – derived from the determination of the principal
chemical constituents of a mineral (eg. CuFeS2)
ELEMENT
ANALYSIS
( wt. %)
ATOMIC
WEIGHT
ATOMIC
PROPORTIONS
ATOMIC
RATIO
RECALCULATED
PERCENTAGE
Cu
34.89
63.54
0.5491
1
34.62
Fe
30.04
55.85
0.53.78
1
30.43
S
34.51
32.07(2)
1.0768
2
34.94
99.44
183.53
100.00
110. CHEMICAL COMPOSITION OF THE EARTH’S
CRUST
Internal structure of the earth:
Core – 2900 to 6370 km.
Inner core – solid (5115 km.)
Outer Core – liquid (2900 km.)
Mantle
Upper mantle – 400 km.
Transition Zone – 1000 km.
Lower Mantle – 2900 km.
Mohorovicic Discontinuity – boundary between the crust and
the upper mantle
Crust - 36 km. thick (under continents), 10-13 km (under oceans)
Upper part – large percentage of sedimentary rocks and
unconsolidated materials forming as thin veneer
Lower part – basement of igneous and metamorphic rocks
Upper 10 mi. consist of 95% igneous rocks, 4% shale, 0.75%
sandstone and 0.25% limestone
111. CHEMICAL COMPOSITION OF THE EARTH’S
CRUST
Average composition – between basalt and granite
Most common elements in the earth’s crust (99%):
ELEMENT
% WEIGHT
% VOLUME
O
46.60
93.77
Si
27.72
0.86
Al
8.13
0.47
Fe
5.00
0.43
Mg
2.09
0.29
Ca
3.63
1.03
Na
2.83
1.32
K
2.59
1.83
112. ROCK-FORMING MINERALS
O constitutes >90% of the volume of the earth’s crust
Earth’s crust is a packing of O anion with interstitial metal
ions, chiefly Si (O-containing minerals such as silicates, oxide
and carbonates most abundant minerals)
Rock-forming minerals are members of silicate-oxidecarbonate group
Economic minerals (eg. Cu, Pb, Hg,) low abundance → locate
areas of high concentrations (ore deposits) to make mining
profitable and to produce metals needed for our economy
Some elements (eg. Rubidium) are dispersed throughout
common minerals and are never concentrated. Rb does not
form specific Rb compounds but is housed in K-rich minerals
Some elements are highly concentrated in some minerals: Zr
in zircon (ZrSiO4), Ti in rutile (TiO2) and ilmenite (FeTiO2)
113. CHEMICAL COMPOSITION OF THE
EARTH
Estimates based on composition of meteorites and the
Estimates based on composition of meteorites and the
volumes of the crust, mantle and core
Core → iron meteorites (FeNi alloy)
Lower mantle → meteorites with 50% metal and 50% silicate
Upper mantle and lower crust → stony silicate meteorites (with little
metal)
ELEMENT
% COMPOSITION
O
29.53
Si
15.20
Al
1.09
Fe
34.63
Mg
12.70
Ca
1.13
Ni
2.39
Na, K, Cr, Co, Mn, P & Ti
0.1 to 1.0
115. CRYSTALLOGRAPHY
Crystallography - study of crystalline solids and the laws that
govern their growth, external shape and internal structure
CRYSTAL – a homogeneous solid possessing long
range, three-dimensional internal order
MINERALS – possess internal ordered arrangement that
is characteristic of crystalline solids
- bounded by smooth plane surfaces and assume
regular geometric forms only when conditions are
favorable
116. CRYSTALLOGRAPHY
Study of structure, symmetry and shape of crystals. This
terminology defines the crystal lattice which provides a
mineral with its ordered internal structure
CRYSTAL:
1. Microcrystalline – fine grained that crystalline nature can
only be determined using a microscope
2. Cryptocrystalline – very fine that individual crystallites
cannot be resolved with microscope but can be detected
by x-ray diffraction
CRYSTAL (perfection of development)
1. Euhedral – perfectly developed faces
2. Subhedral – imperfectly developed faces
3. Anhedral - without faces
AMORPHOUS – lack ordered internal atomic arrangement
(mineraloids)
117. CRYSTALLIZATION
Crystals form from:
Solutions (evaporation of solvent, lowering temperature or
pressure)
Salt dissolved in water → evaporation → solution
contains more and more Na+ and Cl- per unit volume →
remaining water can no longer retain all the salt in
solution → salt begins to precipitate
Slow evaporation → Na+ and Cl- group together and
form one or few large crystals with common
orientation
Rapid evaporation → many centers of
crystallization and form many small randomly
oriented crystals
Melts
Liquid H2O molecules moving freely in any direction →
temperature lowering → molecules become fixed and
arrange themselves in definite order → solid crystalline
mass (ice)
118. CRYSTALLIZATION
Melts
Molten magma → ions of many elements in an
uncombined state → magma cools → various ions are
attracted to one another to form crystal nuclei of the
different minerals → crystallization proceeds with addition
of more ions to the crystal nuclei forming the mineral
grains of the resulting rock
Vapors
Formation of snowflakes → vapor is cooled, the
dissociated atoms or molecules are brought closer
together, eventually locking themselves into crystalline
solid
119. CRYSTAL
A crystal consists of matter that is formed from an ordered
arrangement of atoms, molecules, or ions. Because there
are repeated units, crystals have recognizable structures.
There are seven systems of crystal structures, which are
also called lattices or space lattices.
A crystal or crystalline solid is a solid material, whose
constituent atoms, molecules, or ions are arranged in an
orderly repeating pattern extending in all three spatial
dimensions.
Crystalline structures occur in all classes of materials, with
all types of chemical bonds
120. CRYSTALLOGRAPHIC AXES
In order to study the forms and define the
position of the faces occurring on crystals,
straight lines are assumed to pass through
the ideal center of each crystal. These lines
are called the crystallographic axes.
Intersections of crystallographic axes forms
an axial cross
If the 3 crystal axes are identical (eg.
octahedron), each is referred to the same
letter a. The extremities of the axes are
differentiated by the use of the plus and
minus signs
If the axes are not alike, the one extending
from front to rear is termed the a axis, the
one from left to right the b axis and the
vertical axis as c. They are always referred
to in the following order, a, b, and c
Grouping of crystal forms into 7 crystal
systems is aided by the crystallographic
axes
122. CRYSTALLOGRAPHIC AXES
crystallographic axes can be defined for the various
crystal systems. Two important points to remember:
a.
The lengths of the crystallographic axes are controlled
by the dimensions of the unit cell upon which the
crystal is based.
b.
The angles between the crystallographic axes are
controlled by the shape of the unit cell.
the relative lengths of the crystallographic axes control the
angular relationships between crystal faces. This is true
because crystal faces can only develop along lattice
points. The relative lengths of the crystallographic axes
are called axial ratios.
124. AXIAL RATIO
Axial ratio is defined as the ratio between the lengths of the
axes of crystals. This is normally taken as relative to the
length of the b crystallographic axis. Thus, an axial ratio is
defined as follows:
Axial Ratio = a/b : b/b : c/b
where a is the actual length of the a crystallographic axis, b,
is the actual length of the b crystallographic axis, and c is the
actual length of the c crystallographic
Axial ratios of a given substance is constant
125. AXIAL RATIO
In the cubic system, where the 3 axes are identical, the ratio
is a : a : a or 1 : 1 : 1 (this is usually shorted to 1)
In tetragonal system the lengths the length of the a and b
axes are equal, this reduces to 1 : 1 : c/b (this is usually
shorted to 1 : c)
In hexagonal crystals where there are three equal length
axes (a1, a2, and a3) perpendicular to the c axis this becomes
1 : 1 : 1: c/a (usually shortened to 1 : c)
In orthorhombic, monoclinic and triclinic systems, there are 3
axes of unequal lengths a, b and c. This redices to a/b : 1 :
c/b (this is usually shortened to a : 1 : c)
Modern crystallographers can use x-rays to determine the
size of the unit cell and determine the absolute value of the
crystallographic axes. For example, quartz has the following
unit cell dimensions: a1 = a2 = a3 = 4.913Å and c = 5.405Å
where: Å stands for Angstroms = 10-10 m
126. AXIAL RATIO
Thus the axial ratio for quartz is 1 : 1 : 1 : 5.405/4.913 or
1: 1 : 1 : 1.1001 which simply says that the c axis is 1.1001
times longer than the a axes.
Because crystal faces develop along lattice points, the
angular relationship between faces must depend on the
relative lengths of the axes. Long before x-rays were
invented and absolute unit cell dimensions could be
obtained, crystallographers were able to determine the axial
ratios of minerals by determining the angles between crystal
faces. So, for example, in 1896 the axial ratios of
orthorhombic sulfur were determined to be nearly exactly the
same as those reported above from x-ray measurements.
127.
PARAMETERS AND PARAMETRAL
RATIOS
In order to determine the position of a face on a crystal, it
must be referred to the crystallographic axes
Parametral ratios differ from axial ratios which gives the
numerical lengths of the axes in terms of one of them taken
as unity
128. INTERCEPTS OF CRYSTAL FACES (WEISS
PARAMETERS)
Crystal faces can be defined by their intercepts on the
crystallographic axes. For non-hexagonal crystals, there are
three cases:
1. A crystal face intersects only one of the crystallographic
axes
2. A crystal face intersects two of the crystallographic axes
3. A crystal face that intersects all 3 axes
Two very important points about intercepts of faces:
The intercepts or parameters are relative values, and do
not indicate any actual cutting lengths.
Since they are relative, a face can be moved parallel to
itself without changing its relative intercepts or
parameters
129. CRYSTAL FACE INTERSECTS ONLY ONE
OF THE CRYSTALLOGRAPHIC AXES
As an example the top crystal face shown here intersects
the c axis but does not intersect the a or b axes. If we
assume that the face intercepts the c axis at a distance of 1
unit length, then the intercepts, sometimes called Weiss
Parameters, are: a, b, 1c
130. CRYSTAL FACE INTERSECTS TWO OF
THE CRYSTALLOGRAPHIC AXES
As an example, the darker crystal face shown here
intersects the a and b axes, but not the c axis. Assuming
the face intercepts the a and c axes at 1 unit cell length on
each, the parameters for this face are: 1 a, 1 b, c
131. CRYSTAL FACE THAT INTERSECTS ALL
THREE AXES
In this example the darker face is assumed to intersect the
a, b, and c crystallographic axes at one unit length on each.
Thus, the parameters in this example would be:
1a, 1b, 1c
132. INTERCEPTS OF CRYSTAL FACES
Because one does usually not know the dimensions of the
unit cell, it is difficult to know what number to give the
intercept of a face, unless one face is chosen arbitrarily to
have intercepts of 1. Thus, the convention is to assign the
largest face that intersects all 3 crystallographic axes the
parameters - 1a, 1b, 1c. This face is called the unit face.
For example, in the orthorhombic crystal shown here, the
large dark shaded face is the largest face that cuts all three
axes. It is the unit face, and is therefore assigned the
parameters 1a, 1b, 1c.
133. INTERCEPTS OF CRYSTAL FACES
Once the unit face is defined, the
intercepts of the smaller face can be
determined. These are 2a, 2b,
2/3c. Note that we can divide these
parameters by the common factor 2,
resulting in 1a,1b,1/3c. Again, this
illustrates the point that moving a face
parallel to itself does not change the
relative intercepts. Since intercepts or
parameters are relative, they do not
represent the actual cutting lengths on
the axes.
By specifying the intercepts or parameters of a crystal face, we now have a way
to uniquely identify each face of a crystal. But, the notation is cumbersome, so
crystallographers have developed
another way of identifying or indexing
faces. This conventional notation called
the Miller Index.
134. MILLER INDICES
Miller indices are a notation system in crystallography for
planes and directions in crystal (Bravais) lattices.
Miller Indices are a symbolic vector representation for the
orientation of an atomic plane in a crystal lattice and are
defined as the reciprocals of the fractional intercepts which
the plane makes with the crystallographic axes
In particular, a family of lattice planes is determined by three
integers a, b, and c, the Miller indices. They are written (abc)
and each index denotes an intersection of a plane with a
direction (a, b, c) in the basis of the reciprocal lattice vectors.
By convention, negative integers are written with a bar, as in
3 for −3. The integers are usually written in lowest terms, i.e.
their greatest common divisor should be 1. Miller index 100
represents a plane orthogonal to direction a; index 010
represents a plane orthogonal to direction b, and index 001
represents a plane orthogonal to c.
135. MILLER INDICES
The method by which
indices are determined
is best shown by
example. Recall, that
there are three axes in
crystallographic
systems. Miller indices
are represented by a
set of 3 integer
numbers
136. MILLER INDICES
Steps to describe the
orientation of a crystal face or
a plane of atoms within a
crystal lattice:
1. The first thing that must be
ascertained are the
fractional intercepts that
the plane/face makes with
the crystallographic axes.
In other words, how far
along the unit cell lengths
does the plane intersect
the axis. In the figure on
the right, the plane
intercepts each axis at
exact one unit length.
137. MILLER INDICES
2.
3.
4.
Taking the reciprocal of the fractional intercept of each unit length
for each axis. In the figure on the
right, the values are all 1/1.
Finally the fractions are cleared
(i.e., make 1 as the common
denominator).
These integer numbers are then
parenthetically enclosed and
designate that specific crystallographic plane within the lattice.
Since the unit cell repeats in space,
the notation actually represents a
family of planes, all with the same
orientation. In the figure, the Miller
indices for the plane is (111)
140. INTERNAL ORDER AND CRYSTAL
MORPHOLOGY
3-D internal order of a crystal – considered as a repetition of
a motif* in such a way that the environment of and around
each repeated motif is identical
Motifs:
Anionic groups (SiO4)-4
Ions (Ca2+, Mg2+, Fe2+)
Ordered arrangement provides more stable and less
energetic configuration. An ordered pattern is generated by
a motif repeated in a regular sequence of new location
Any motion that brings the original motif into coincidence
with the same motif elsewhere in the pattern is referred to as
an operation. Thus a homogeneous pattern can be generated from a single motif by a set of geometric operations.
molecules (H2O)
141. INTERNAL ORDER AND CRYSTAL
MORPHOLOGY
3-D internal order of a crystal – considered as a repetition of
a motif in such a way that the environment of and around
each repeated motif* is identical
Motifs:
Anionic groups (SiO4)-4
molecules (H2O)
Ions (Ca2+, Mg2+, Fe2+)
Symmetry** - describes the repetition of structural features
1. Translational symmetry - describes the periodic repetition
of a structural feature across a length or through an area
or volume
2. Point symmetry - describes the periodic repetition of a
structural feature around a point (reflection, rotation,
inversion)
142. INTERNAL ORDER AND CRYSTAL
MORPHOLOGY
Lattice - a network or array composed of single motif which
has been translated and repeated at fixed intervals
throughout space (imaginary)
- directly related to the idea of translational symmetry
- eg. square → planar square lattice
Unit cell of a lattice - the smallest unit which can be repeated
in three dimensions in order to construct the lattice
- consists of a specific group of atoms which are bonded to
one another in a set geometrical arrangement.
- this unit and its constituent atoms are then repeated over
and over in order to construct the crystal lattice. The
surroundings in any given direction of one corner of a unit
cell must be identical to the surroundings in the same
direction of all the other corners. The corners of the unit
cell therefore serve as points which are repeated to form
a lattice array
143. INTERNAL ORDER AND CRYSTAL
MORPHOLOGY
Lattice points - corners of the unit cell that serve as points
which are repeated to form a lattice array
5 possible lattices in a plane (translation)
1. square unit cell
2. rectangular unit cell
3. centered rectangular unit cell
4. parallelogram
5. hexagonal unit cell - rhombus
144. BRAVAIS LATTICES
French crystallographer Auguste Bravais (1811-1863)
established that in three-dimensional space only fourteen
different lattices may be constructed → 6 CRYSTAL
SYSTEMS
3 Types of Bravais Lattices:
primitive lattice - has only a lattice point at each corner of
the three-dimensional unit cell
body-centered lattice - contains not only lattice points at
each corner of the unit cell but also contains a lattice point
at the center of the three-dimensional unit cell
face-centered lattice - possesses not only lattice points at
the corners of the unit cell but also at either the centers of
just one pair of faces or else at the centers of all three
pairs of faces
146. POINT SYMMETRY
Point symmetry - describes the repetition of a motif or
structural feature around a single reference point, commonly
the center of a unit cell or a crystal
Point Symmetry Operations:
Reflection - structural features on one side of a plane
passing through the center of a crystal are the mirror
image of the structural features on the other side. The
plane across which the reflection occurs is then termed a
mirror plane
Rotation - structural element is rotated a fixed number of
degrees about a central point and then repeated. A
square, for example, possesses 4-fold rotational
symmetry because it may be rotated four times by 90°
about its central point before it is returned to its original
position. Each time it is rotated by 90° the resultant
square will be identical in appearance to the original
square
147. POINT SYMMETRY
Point Symmetry Operations:
Inversion - any line which is drawn through the origin at
the center of the crystal will connect two identical features
on opposite sides of the crystal.
Rotoinversion - compound symmetry operation which is
produced by performing a rotation followed by an
inversion
reflection, rotation, inversion and rotoinversion symmetry
operations → combined in different ways → 32 different
possible combinations of these symmetry elements → 32
crystal classes → corresponds to a unique set of symmetry
operations → each crystal class → placed into one of 6
crystal systems
149. CRYSTAL SYSTEMS
ISOMETRIC or CUBIC
the crystallographic axes used in this system are of equal
length and are mutually perpendicular, occurring at right
angles to one another
all crystals of the isometric system possess four 3-fold
axes of symmetry, each of which proceeds diagonally
from corner to corner through the center of the cubic unit
cell
may also demonstrate up to three separate 4-fold axes of
rotational symmetry or six 2-fold axes of symmetry
minerals of this system may demonstrate up to nine
different mirror planes
Minerals of this system tend to produce crystals of
equidimensional or equant habit
Examples: halite, magnetite and garnet.
151. CRYSTAL SYSTEMS
HEXAGONAL
minerals of the hexagonal crystal system are referred to
three crystallographic axes which intersect at 60° and a
fourth which is perpendicular to the other three. This fourth
axis is usually depicted vertically.
crystals of the hexagonal division possess a single 6-fold
axis of rotation. In addition to the single 6-fold axis of
rotation, crystals of the hexagonal division may possess
up to six 2-fold axes of rotation. They may demonstrate a
center of inversion symmetry and up to seven mirror
planes. Crystals of the rhombohedral division all possess
a single 3-fold axis of rotation rather than the 6-fold axis of
the hexagonal division.
minerals of this division tend to produce hexagonal prisms
and pyramids
apatite, beryl and high quartz (hexagonal); calcite,
dolomite, low quartz and tourmaline (rhombohedral).
153. CRYSTAL SYSTEMS
TETRAGONAL
minerals of the tetragonal crystal system are referred
to three mutually perpendicular axes. The two
horizontal axes are of equal length, while the vertical
axis is of different length and may be either shorter or
longer than the other two
minerals of this system all possess a single 4-fold
symmetry axis. They may possess up to four 2-fold
axes of rotation, a center of inversion, and up to five
mirror planes
minerals tend to produce short crystals of prismatic
habit
zircon and cassiterite
155. CRYSTAL SYSTEMS
ORTHORHOMBIC
Minerals of the orthorhombic crystal system are referred to
three mutually perpendicular axes, each of which is of a
different length than the others
Crystals of this system uniformly possess three 2-fold
rotation axes and/or three mirror planes. The holomorphic
class demonstrates three 2-fold symmetry axes and three
mirror planes as well as a center of inversion. Other
classes may demonstrate three 2-fold axes of rotation or
one 2-fold rotation axis and two mirror planes
Crystals of this system tend to be of prismatic, tabular, or
acicular habit
olivine and barite.
157. CRYSTAL SYSTEMS
MONOCLINIC
Crystals of the monoclinic system are referred to three
unequal axes. Two of these axes are inclined toward each
other at an oblique angle; these are usually depicted
vertically. The third axis is perpendicular to the other two.
The two vertical axes therefore do not intersect one
another at right angles, although both are perpendicular to
the horizontal axis
Monoclinic crystals demonstrate a single 2-fold rotation
axis and/or a single mirror plane. The holomorphic class
possesses the single 2-fold rotation axis, a mirror plane,
and a center of symmetry. Other classes display just the 2fold rotation axis or just the mirror plane
minerals of the monoclinic system tend to produce long
prisms
pyroxene, amphibole, orthoclase, azurite, and malachite
159. CRYSTAL SYSTEMS
TRICLINIC
Crystals of the triclinic system are referred to three
unequal axes, all of which intersect at oblique angles.
None of the axes are perpendicular to any other axis
Crystals of the triclinic system may be said to possess
only a 1-fold symmetry axis, which is equivalent to
possessing no symmetry at all. Crystals of this system
possess no mirror planes. The holomorphic class
demonstrates a center of inversion symmetry
tend to be of tabular habit
plagioclase and axinite
161. CRYSTAL FORMS
Crystal Forms - set of faces which are geometrically
equivalent and whose spatial positions are related to one
another according to the symmetry of the crystal
1.
Monohedron or pedion
2.
Parallelohedron or pinacoid
3.
Dihedron, or dome
4.
Sphenoid
5.
Disphenoid
6.
Prism
7.
Pyramid
8.
Dipyramid
9.
Trapezohedron
10. Scalenohedron
11. Rhombohedron
12. Tetrahedron
13. 15 under the isometric system
164. BASIS FOR MINERAL CLASSIFICATION
Classification of minerals based on chemical composition
Dependent on the dominant anion* or anionic group (eg.
oxides, halides, silicates etc.)
Reasons for using chemical composition as basis for
classification:
Minerals having the same anion or anionic group
dominant in their composition have unmistakable family
resemblances, in general stronger and more clearly
marked than those shared by minerals containing the
same dominant cation (eg. Carbonates resemble each
other more closely that the minerals of copper)
Minerals related by dominance of the same anion tend to
occur together or in the same or similar geologic
environment (eg. Sulfides occur in close mutual
association in deposits of vein or replacement type,
silicates make the bulk of the earth’s rocks)
Agrees well with current chemical practice in naming and
classifying inorganic compounds
165. BASIS FOR MINERAL CLASSIFICATION
Crystallochemical principles – mineral classification must be
based on:
Chemical composition
Internal structure
Large classes are further divided into subclasses on the
basis of internal structure:
Silicate class→ { framework silicate subclass (structural
{ chain silicate subclass
(arrangement
{ sheet silicate subclass
(of SiO4
↓
family (chemical type)
↓
group (structural similarity)
↓
species → series → variety
166. NATIVE ELEMENTS
≈ 20 elements in native state (excluding free gasses)
Types of Native Elements:
Metals
Semimetals
Nonmetals
167. NATIVE ELEMENTS
Native Metals
Usefulness of metals arose from the chance discovery of
nuggets and masses of gold
Early cultures use metals in native state
Groups of Native Metals:
Gold Group
Platinum Group
Iron Group
168. NATIVE ELEMENTS
Gold Group
Belong to the same group in the periodic table of
elements and have similar chemical properties
Sufficiently inert to occur in an elemental state in nature
Minerals are isostructural and are built on the facecentered lattice
Common Properties:
Soft, malleable, ductile and sectile
Excellent conductors of heat and electricity
Display metallic luster and hackly fracture
Have low melting points
All are isometric hexoctahedral
Have high densities resulting from close cubic packing
Gold (Au), silver (Ag), copper (Cu), Lead (Pb)
Differing properties due to atomic properties (specific
gravity, color: yellow of Au, red of Cu and white of Ag)
170. NATIVE ELEMENTS
Native Semimetals
Arsenic (As), antimony (Sb) and bismuth (Bi)
Belong to an isostructural group with space group R3m
Unlike native metals, these cannot be represented as a
simple packing of spheres, because each atom is
somewhat closer to three of its neighbors than to the
remainder of the surrounding atoms. Bonding of the 4
closest atoms is covalent
Bond type between metallic and covalent, hence, it is
stronger and more directional than pure metallic elements
Brittle and much poorer conductors of heat and electricity
than the native metals
171. NATIVE ELEMENTS
Native Non Metals
Sulfur (S), diamond (C) and graphite (C)
Structure very different from the native metals
172. NATIVE ELEMENTS
GOLD (Au)
Crystallography:
Isometric crystal system
octahedral form
Often in arborescent crystal
groups
Crystal are irregularly
formed from filiform to
reticulated to dendritic
Seldom show crystal forms,
often in irregular plates,
scales or masses
Hardness: 2.5 to 3
Specific Gravity: 19.3 (pure)
Fracture: hackly
Tenacity: Malleable, ductile
Luster: metallic opaque
173. NATIVE ELEMENTS
GOLD (Au)
Color: various shades of
yellow becoming paler with
increase in silver
Composition and Structure:
Most gold contains Ag
When Ag >20% → electrum
Small amounts of Cu, Fe and
traces of Bi, Pb, Sn, Zn and
Platinum metals
Purity or “fineness” of gold is
expressed in “parts per 1000”
Most gold contains about 10%
of other metals and has a
fineness of 900
Structure of gold is based on
cubic closest packing Au
Diagnostic Features:
Distinguished from yellow
sulfides pyrite and
chalcopyrite and from
yellow flakes of altered
micas by its sectility and
high specific gravity
Fuses at 1063°C
Soluble in aqua regia (1:3
volume HNO3 and HCl
Occurrence:
Rare element but widely
distributed in small amounts
Most commonly found in in
veins that bear genetic
relation to silicic types of
igneous rocks
174. NATIVE ELEMENTS
GOLD (Au)
Most gold occur in native
metal
If in combination → only with
tellurium and selenium
Chief source of gold are
hydrothermal gold-quartz
veins with pyrite and other
sulfides deposited from
ascending mineral solutions
where gold is only
mechanically mixed with
sulfides and is not in chemical
substitution. At or near the
surface, of the earth,
oxidation of the gold-bearing
sulfides sets the gold free,
making its extraction easy by
amalgamation (finely crushed
ore is washed over copper
plates coated with mercury)
When sulfides are present in
any quantity, not all gold can
be recovered by
amalgamation → cyanide or
chlorination process is used
CYANIDATION → finely
crushed ore is treated with a
solution of potassium or
sodium cyanide, forming a
soluble cyanide. The gold is
then recovered by
precipitation with zinc or by
electrolysis
CHLORINATION → renders
gold in a soluble form by
treating the crushed and
roasted ore with chlorine
175. NATIVE ELEMENTS
GOLD (Au)
When gold-bearing veins are
weathered, the liberated gold
either remains in the soil
mantle as “eluvial deposit” or
is washed into the
neighboring streams to form
“placer or alluvial gold”.
Because of its high specific
gravity, gold works its way
through the lighter sands and
gravels to lodge behind
irregularities or in crevices in
bedrock. Gold is recovered by
panning or washing through
sluice boxes where gold
collects behind cross-bars
and amalgamates with
mercury placed behind the
cross-bars
Uses: monetary standard,
jewelry, scientific instru-ments,
electroplating, gold leaf, dental
appliances, small gold bars for
investment purposes
176. NATIVE ELEMENTS
SILVER (Ag)
Crystallography:
Isometric crystal system
Crystals commonly malformed and in branching
arborescent or reticulated
groups
Usually in irregular masses,
plates and scales, in other
places as fine or coarse
wires
Hardness: 2.5 to 3
Specific gravity: 10.5 (pure)
Fracture: hackly
Tenacity: Malleable and ductile
Luster: metallic
Color and streak: silver white
and tarnish to brown or gray
black
177. NATIVE ELEMENTS
SILVER (Ag)
Composition and Structure:
Frequently contains alloyed
Au, Hg, and Cu. Rare traces
of Pt, Sb and Bi
Amalgam is a solid solution of
Ag and Hg
Structure is based on closest
packing of Ag atoms
Diagnostic features:
Silver can be distinguished by
its malleability, color on fresh
surface and high specific
gravity
Fusible at 960°C to a bright
globule
Occurrence: widely distributed
in small amounts in the oxidized
zones of ore deposits
Native silver in larger
deposits is the result of
deposition from primary
hydrothermal solutions
Uses: photographic film
emulsions, plating, brazing
alloys, tableware, electronic
equipment, coinage
178. NATIVE ELEMENTS
COPPER (Cu)
Crystallography:
Isometric crystal system
Tetrahexahedron, cube,
dodecahedron, octahedron
Usually malformed and in
branching and arborescent
groups
Usually occurs in irregular
masses, plates and scales
and in twisted wire-like forms
Hardness: 2.5 to 3
Specific gravity: 8.9
Fracture: hackly
Tenacity: highly malleable and
ductile
Luster: metallic
179. NATIVE ELEMENTS
COPPER (Cu)
Composition and Structure:
Contains small amounts of
Ag, Bi, Hg, As and Sb
Structure is based on cubic
closest packing of Cu atoms
Diagnostic Features:
Recognized by its red color
on fresh surfaces, hackly
fracture, high specific gravity
and malleability
Fuses at 1083°C to globule
Dissolves readily in nitric acid
and the resulting solution is
colored deep blue on addition
of an excess ammonium
hydroxide
Occurrence:
small amounts found in
oxidized zones of copper
deposits associated with
cuprite, malachite and
azurite in many localities
Most primary deposits of
native copper are associated
with basaltic lavas, where
deposition of copper
resulted from the reaction of
hydrothermal solutions with
iron oxide minerals
Only major deposit is found
in Precambrian basic lava
flows in the Keweenaw
Peninsula, Michigan
180. NATIVE ELEMENTS
COPPER (Cu)
Use: minor ore of copper,
electrical purposes (wires),
alloys:
Brass (copper and zinc)
Bronze (copper and tin with
zinc)
German silver (copper, zinc
and nickel)
181. NATIVE ELEMENTS
PLATINUM (Pt)
Crystallography:
Isometric crystal system
Commonly malformed
Usually in small grains and
scales, in some places as
irregular masses and nuggets
Hardness: 4 to 4.5 (unusually high
for metal)
Specific Gravity: 21.45 (pure)
Tenacity: Malleable, ductile
Luster: bright metallic
Color: steel gray
Composition and Structure:
Usually alloyed with several
percent Fe (making it
magnetic when iron-rich) and
182. NATIVE ELEMENTS
PLATINUM (Pt)
amounts of Ir, Os, Rh, Pd,
Cu, Au, Ni
Structure of platinum is
based on the cubic closest
packing of Pt atoms
Diagnostic Features:
determined by its high
specific gravity, malleability,
infusibility in the blowpipe
flame and insolubility except
in aqua regia
Occurrence:
most occur as native metal in
ultrabasic rocks especially
dunites associated with
olivine, chromite, pyroxene
and magnetite
Occur as placers highly close
to the platinum-bearing
igneous parent rock
First discovered in the United
States of Colombia, South
America
Uses: catalyst in the chemical and
petroleum industries, chemical
apparatus, electrical equipment,
jewelry, dentistry, surgical
instruments, pyrometry and
photography
183. NATIVE ELEMENTS
IRON (Fe)
Crystallography:
Isometric crystal system
Crystals are rare
Terrestrial – in blebs and
large masses
Meteoric (kamacite) – in
plates and lamellar masses
Hardness: 4.5
Specific Gravity: 7.3-7.9
Fracture: hackly
Tenacity: malleable
Luster: metallic opaque
Color: steel gray to black
Magnetism: strongly magnetic
Composition and Structure:
Always contains some Ni
and frequently small
amounts of Co, Cu, Mn, S
and C
184. NATIVE ELEMENTS
IRON (Fe)
Kamacite contains approx.
5.5. weight percent Ni while
Taenite has 27-65 weight
percent Ni
Structure is based on bodycentered cubic packing of
atoms
Diagnostic Features: Strong
magnetism, malleability and the
oxide coating on its surface.
Infusible but soluble in HCLl
Occurrence:
Seldom as terrestrial iron but
common in meteorites
Elemental iron is highly
unstable in oxidizing
conditions
Normally present as Fe2+ or
Fe3+ in oxides in magnetite
(Fe3O4) or hematite (Fe2O3) or
goethite (FeO.OH)
Terrestrial iron regarded as
primary magmatic
constituent or a s
asecondary product formed
from the reduction of iron
compounds by assimlated
carbonaceous material
Most important occurrence
is in Disko Is., Greenland
185. NATIVE ELEMENTS
ARSENIC (As)
Crystallography:
Hexagonal crystal system
Pseudocubic crystals rare
Usually granular massive,
reniform and stalactitic
Cleavage: perfect at {0001}
Hardness: 3.5
Specific Gravity: 5.7
Tenacity: brittle
Luster: nearly metallic
Color: tin-white on fresh fracture,
tarnishes to dark gray on
exposure
Streak: gray
Composition and Structure:
Often shows limited
substitution by Sb
Diagnostic Features:
Diagnostic blowpipe and
chemical tests
Occurrence:
Comparatively rare. Found
in veins in crystalline rocks
associated with Ag, Co, or Ni
Uses: very minor ore of arsenic
186. NATIVE ELEMENTS
BISMUTH (Bi)
Crystallography:
Hexagonal crystal system
Distinct crystals are rare
Usually laminated and
granular, maybe reticulated or
arborescent
Cleavage: perfect at {0001}
Hardness: 2 to 2.5
Specific Gravity: 9.8
Tenacity: sectile, brittle
Luster: metallic
Color: reddish silver-white
Streak: shining silver-white
Composition and Structure:
Small amounts of As, S, Te
and As maybe present
Structure similar to As and
Sb
Diagnostic Features:
Recognized chiefly by
laminated nature, reddishsilver color, perfect cleavage
and sectility
Fusible at 271°C
Diagnostic blowpipe tests
Occurrence:
Rare, occurring with ores of
Ag, Co, Ni, Pb and Sn
Uses: chief ore of bismuth, used
for electrical fuses and safety
plugs in water sprinkling
systems, medicine, cosmetics
187. NATIVE ELEMENTS
SULFUR (S)
Crystallography:
Orthorhombic crystal system
Pyramidal habit common
Commonly found in irregular
masses, massive, reniform,
stalactitic
Hardness: 1.5 to 2.5
Specific Gravity: 2.05 to 2.09
Fracture: conchoidal to uneven
Tenacity: brittle
Color: sulfur-yellow, varying with
impurities
Transparent to translucent
Poor conductor of heat
When sample is held in hand
close to the ear, it can be heard
To crack due to expansion of
surface layers due to heat from
hand
Composition and Structure:
May contain small amounts
of Se
Diagnostic Features:
Recognized by its yellow
color and ease with which it
burns
Absence of good cleavage
distinguishes it from
orpiment
Fusible at 112.8°C and
burns with a blue flame with
sulfur dioxide
Sublimates in closed tube
Occurrence:
Occurs at or near crater rims
of active or inactive
volcanoes where it is
188. NATIVE ELEMENTS
SULFUR (S)
From the gases given off in
fumaroles. These may furnish
sulfur as a direct sublimation
product or by incomplete
oxidation of hydrogen sulfide
gas
It is also formed from sulfates,
by the action of sulfur-forming
bacteria
Maybe found in veins
associated with metallic
sulfides and formed by the
oxidation of the sulfides
Uses: chemical industry chiefly in
the manufacture of sulfuric acid,
fertilizers, insecticides,
explosives, coal tar products,
rubber, preparation of wood
pulp for paper manufacture
189. NATIVE ELEMENTS
DIAMOND (C)
Crystallography:
Isometric crystal system
Crystals usually octahedral
but maybe cubic or
dodecahedral
“Bort” variety has rough
exterior resulting from radial
or cryptocrystalline aggregate
(without gem value)
Hardness: 10
Cleavage: perfect {111}
Specific gravity: 3.51
Luster: adamantine, uncut
crystals have a characteristic
greasy appearance
Color: usually pale yellow or
colorless, pale red, green, blue
“Carbonado” is black or grayish
black bort, noncleavable,
opaque and less brittle than
crystals
Composition and Structure:
Pure carbon
Diagnostic Features:
Hardness, adamantine luster
and cleavage
Insoluble in acids and alkalis
At high temperature in
oxygen, will burn to CO2 gas
leaving no ash
Occurrence:
Found in alluvial deposits,
where it accumulates
because of its inert chemical
nature, great hardness and
fairly high specific gravity
In Africa and Siberia, they
190. NATIVE ELEMENTS
DIAMOND (C)
Occur in situ hosted in
altered peridotite called
kimberlite or “diamond pipes”
First found in India
Uses: fragments are used to cut
glass, grinding and polishing
diamonds and other gemstones,
cutting rocks, diamond drilling,
gemstones-value depends on the
color and purity, skill by which it
was cut and its size (1 carat=0.2
g.)
191. NATIVE ELEMENTS
GRAPHITE (C)
Crystallography:
Hexagonal crystal system
Usually tabular
Hardness: 1-2 (readily marks
paper and soils fingers)
Specific Gravity: 2.23
Fracture: hackly
Luster: metallic to dull
Color: black
Streak: black
Greasy feel
Composition and Structure:
Carbon
Diagnostic Features:
Color, foliated nature and
greasy feel, unattacked by
acids, infusible but may burn
to CO2
Occurrence:
Mostly occurs in
metamorphic rocks such as
marble, gneiss and schist
derived from the
carbonaceous material of
organic origin that has been
converted into graphite
during metamorphism.
Metamorphosed coal beds
may be partially converted
into graphite during
metamorphism
Uses: manufacture of refractory
crucibles for steel, brass and
bronze industries, lubricant
(mixed with oil) pencil lead
(mixed with fine clay, protective
paint for structural steel,
batteries, electrodes and
generator brushes
192. NATIVE ELEMENTS
GRAPHITE (C)
Uses: manufacture of
refractory crucibles for steel,
brass and bronze industries,
lubricant (mixed with oil)
pencil lead (mixed with fine
clay, protective paint for
structural steel, batteries,
electrodes and generator
brushes
193. SULFIDES
An important class of minerals that includes the majority of
the ore minerals
Sulfide class also includes the sulfarsenides, arsenides
and tellurides
Most sulfides are opaque with distinctive colors and
characteristic colored streaks
General formula of sulfides is XmZn in which X represents
the metallic elements and Y the nonmetallic element
Many of the sulfides have ionic and covalent bonding
whereas others, displaying most of the properties of
metals, have metallic bonding
194. SULFIDES
ACANTHITE (Ag2S)
Crystallography:
Monoclinic crystal system
Crystals commonly cubic
Most commonly massive or
as coating
Hardness: 2 to 2.5
Specific Gravity: 7.3
Tenacity: very sectile, can be cut
by a knife like lead
Luster: metallic
Color: black
Streak: black, shining
Bright on fresh surface but on
exposure becomes dull black,
owing to the formation of an
earthy sulfide
also known as ARGENTITE
Composition and Structure:
Ag (87.1%), S (12.9%),
commonly contains
impurities such as calcium
and magnesium sulfates and
calcium and magnesium
chlorides
Diagnostic Features:
Distinguished by its color,
sectility and high specific
gravity
Occurrence:
An important primary silver
mineral found in veins
associated with native silver,
the ruby silvers, galena and
sphalerite
196. SULFIDES
CHALCOCITE (Cu2S)
Crystallography:
Orthorhombic crystal system
Crystals are very rare
Commonly fine-grained and
massive
Cleavage: poor {110}
Fracture: conchoidal
Hardness: 2.5 to 3
Specific Gravity: 5.5 to 5.8
Tenacity: imperfectly sectile
Luster: metallic
Color: shining lead gray
tarnishing to dull black on
exposure
Streak: grayish black
Some chalcocite are soft and
sooty
Composition and Structure:
Cu (79.8%), S (20.0%), may
contain small amounts of Ag
and Fe
Diagnostic Features:
Distinguished by its lead
gray color and sectility.
When heated on charcoal it
gives odor of SO2
Occurrence:
One of the most important
copper-ore mineral
Principal occurrence is as a
supergene mineral in
enriched zones of sulfide
deposits (under surface
conditions the primary
copper sulfides are oxidized
197. SULFIDES
CHALCOCITE (Cu2S)
The soluble sulfates formed
above move downward
reacting with the primary
minerals to form chalcocite
and thus enriching the ore in
copper. The water table is the
lower limit of the zone of
oxidation and here a chalocite
blanket may form)
May also occur as primary
mineral in in veins with
bornite, chalcopyrite, enargite
and pyrite
Much of the world’s copper is
produced from “porphyry
copper”. In porphyry copper,
primary copper minerals are
disseminated through the rock
Uses: important ore of copper