1. Minerals and Rocks
Chapter 5

2. Outline
• Minerals and rocks
-What are minerals? Geologic definition, significance.
-What are rocks? Geologic definition, 3 main types.
• Mineral structure
-Crystalline structure, crystals, crystal lattice
-Determining atom arrangement (XRD), atomic bonding
-Polymorphs, crystal growth and packing of atoms
• Physical properties of minerals
-Overview: common ones, less common ones
-Color, streak, luster, hardness, specific gravity, crystal habit/form,
fracture, and cleavage
• Mineral classes and silicates
-Mineral classes, most importantly silicates
-Silica tetrahedra building block
-Silicate types: from individual tetrahedra to framework Chapter 5 5
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3. Minerals
• The “building blocks” of rocks, and hence, of Earth.
• -more than 4000 are known
• -dozens of new minerals are discovered annually
•
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4. Minerals
• Societies depend on mineral resources.
• Metals: iron, copper, lead, zinc, nickel, aluminum, etc.
• Non-metals: gypsum, limestone, clay
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5. Minerals
• Economically important – Drive world economies.
• Historically important – Dictated human history.
• Iron.
• Copper.
• Gold.
• Diamonds.
• Gems.
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6. Mineral Definition
• Geologic definition of a mineral is specific.
• A naturally occuring solid, formed geologically, that has
a crystal structure and a specific chemical composition,
and is usually inorganic
• -doesn’t include “minerals in nutritional sense
• -A mineraloid exhibits some, but not all, properties
Gypsum
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7. Rocks
• Rocks are Earth materials made from minerals.
• Most rocks have more than one kind of mineral.
• -example: granite
• -mineral(s)?
• Potassium, quartz, hornblende
• -some are mono-mineralic
• Limestone (calcite), rock salt
• (halite), glacial ice
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8. Rock Definition
• Geologists definition: coherent, naturally occuring solid
made up of an aggregate of minerals (or more
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9. 3 Main Rock Types
1. Igneous – solidified from molten rock or melt
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10. 3 Main Rock Types
2. Sedimentary
3. -cemented/precipitated from rock fragments/solution
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11. 3 Main Rock Types
3. Metamorphic – existing rock altered by changes in
pressure and temperature
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12. Outline
• Minerals and rocks
-What are minerals? Geologic definition, significance.
-What are rocks? Geologic definition, 3 main types.
• Mineral structure
-Crystalline structure, crystals, crystal lattice
-Determining atom arrangement (XRD), atomic bonding
-Polymorphs, crystal growth and packing of atoms
• Physical properties of minerals
-Overview: common ones, less common ones
-Color, streak, luster, hardness, specific gravity, crystal habit/form,
fracture, and cleavage
• Mineral classes and silicates
-Mineral classes, most importantly silicates
-Silica tetrahedra building block
-Silicate types: from individual tetrahedra to framework Chapter 5 5
Chapter

13. Crystalline Structure
• A solid with disordered atoms is called a glass
Glass
• Atoms in a mineral are specifically ordered
• Crystalline structure based on atomic patterns
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14. Crystals
• Minerals displaying flat external faces (rare).
• -crystal faces form best in open cavities
• -crystals are often prized mineral specimens
Beryl Quartz
Green, gem version -> emerald
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15. Crystals
• Constancy of angles between crystal faces.
• -same mineral always (ideal) has same crystal faces
• -adjacent faces occur at regular (diagnostic) angle
• Faces and angles reflect the atomic arrangement.
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16. Crystal Lattice
• Ordered atoms in crystals form a lattice.
• Lattices are patterns that repeat in 3D
• This internal pattern controls mineral properties.
• -crystal shape
• -planes of symmetry
•
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17. Determining Atom Arrangements
• X-Ray Diffraction (XRD) probes crystal lattices.
• Unique lattice spacing is used to ID minerals.
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18. Bonding of Atoms
• Lattice atoms are held in place by atomic bonds.
 Bond characteristics govern mineral properties.
• 5 recognized types of bonds (Appendix A).
• -covalent (gain/loose )
• -metallic
• -van
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19. Polymorphs (many + form)
• Same composition but different crystal structure.
• Polymorphs show the importance of bond type.
• Diamond and graphite are carbon polymorphs (C)
• -diamond: strong covalent bonds; hardest mineral
• -graphite: weak van der waals bonds; softest mineral
Diamond
Graphite
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20. Crystal Growth
• Crystals grow as atoms attach to mineral surfaces
• -growth starts from a central seed crystal
• -growth expands outward
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21. Crystal Growth
• Outward crystal growth fills available space.
• Resulting crystal shape governed by surroundings.
• -open space: good crystal faces grow
• -confined space: no crystal spaces
• Crystals mostly grow by…
• Solidification from a melt
• Precipitation from solution
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22. Atomic Packing
• Ion size (radius) and charge control packing.
• Ion – atom charged due to gain or loss of an electron
• Cation – positive ion due to loss of electron
• Anion – negative ion due to gain of electron
• Ionic radii due to # of electrons; anions are bigger.
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23. Atomic Packing
• Anions and cations bond to neutralize charges.
• Anion – Cation “fit” governed by relative size.
• -large central cation – larger number of anions
• -smalll central cation – smaller number of anions
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24. Outline
• Minerals and rocks
-What are minerals? Geologic definition, significance.
-What are rocks? Geologic definition, 3 main types.
• Mineral structure
-Crystalline structure, crystals, crystal lattice
-Determining atom arrangement (XRD), atomic bonding
-Polymorphs, crystal growth and packing of atoms
• Physical properties of minerals
-Overview: common ones, less common ones
-Color, streak, luster, hardness, specific gravity, crystal habit/form,
fracture, and cleavage
• Mineral classes and silicates
-Mineral classes, most importantly silicates
-Silica tetrahedra building block
-Silicate types: from individual tetrahedra to framework Chapter 5 5
Chapter

25. Physical Properties of Minerals
• Characteristics determined by your senses.
• Used to ID minerals.
• Properties depend upon…
• -chemical composition
• -crystal structure
Some are diagnostic.
i.e. pyrite (fes2) Pyrite
-minerals have a unique
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26. Physical Properties
• Common properties:
• Color.
• Streak.
• Luster.
• Hardness.
• Specific gravity.
• Crystal habit (ideal shape).
• Crystal form.
• Fracture.
• Cleavage.
Needle-like crystal habit
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27. Physical Properties
• Less common physical properties:
• Taste. Magnetite crystals on a large magnet.
• Smell.
• Feel.
• Magnetism.
• Effervescence.
• Refractive index.
• Malleability.
Calcite effervesces with acid
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28. Color
• Color is diagnostic for some minerals.
• E.g. olivine/malachite is always green, azurite is always
blue
Some minerals may exhibit a broad color range.
-quartz (clear, white, yellow, pink, purple
Quartz – Many colors Malachite – always green
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29. Streak
• Color of a mineral struck across unglazed porcelain.
• Streak is often a useful diagnostic property.
• Congruent streak –streak color same as mineral
• -magnetite: black mineral; black streak
Incongruent streak – streak color different than mineral
-chromite: black mineral; greenish-brown streak
Hematite – Red-brown streak
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30. Luster
• The way a mineral scatters light.
• Two subdivisions.
• Metallic – Looks like a metal.
• Nonmetallic.
• Vitreous (glassy).
• Satiny.
• Silky.
• Resinous.
• Pearly. Quartz – Vitreous luster
• Earthy (dull).
• Adamantine (brilliant).
Satin spar Gypsum – Satiny luster
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31. Hardness
• Scratching resistance of a mineral.
• Hardness compared to Mohs Hardness Scale.
1. Talc, Graphite
2. Gypsum
Fingernail 2.5
3. Calcite
Copper Penny 3.5
4. Fluorite
5. Apatite
Glass - Steel 5.5
6. Orthoclase
Steel File 6.5
7. Quartz
8. Topaz
9. Corundum
10. Diamond
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32. Specific Gravity
• Related to density (mass per volume).
• Mineral weight over weight of equal water volume.
• Specific gravity is heft – how heavy it feels
• -pyrite: heavy (sg 5.0)
• -feldspar: light (sg 2.6)
• -pyrite feels heavier
Pyrite Potassium Feldspar
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33. Crystal Habit
• Crystal habit is the ideal shape of crystal faces.
• -ideal growth requires ideal conditions
• -many terms are used to describe habit
Cubes Octahedra Blades Hexagonal Prisms
Dodecahedra Rhombohedra Tetragonal Prisms
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34. Crystal Form
• Minerals vary in crystal face development.
• Euhedral – good crystal faces; gown in open cavity
• Anhedral – no crystal faces; grown in tight space
• Subhedral – between the two
• Face development indicates growth history
• Anhedral crystals common; euhedral less so.
Amethyst Geode
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35. Fracture
• Some minerals lack planes of weakness.
• Due to equal molecular bonds in all directions.
• These minerals fracture and hence don’t have cleavage.
• Example: Quartz
Obsidian
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36. Cleavage
• Tendency to break along planes of weakness.
• Due to equal molecular bonds in all directions.
• These minerals fracture and hence don’t have
cleavage.
• i.e. quartz displays conchoidal fracture
• -shaped like inside of a clam shell
• -breaks along smooth curved surfaces
• -cleavage produces flat surfaces
• -described by number of planes and their angles
• Sometimes mistaken for crystal habit. Chapter 5

37. Cleavage
• Examples of Cleavage:
Muscovite Mica
• 1 direction
• 2 directions at 90º
Potassium Feldspar
• 2 directions NOT at 90º
Amphibole
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38. Outline
• Minerals and rocks
-What are minerals? Geologic definition, significance.
-What are rocks? Geologic definition, 3 main types.
• Mineral structure
-Crystalline structure, crystals, crystal lattice
-Determining atom arrangement (XRD), atomic bonding
-Polymorphs, crystal growth and packing of atoms
• Physical properties of minerals
-Overview: common ones, less common ones
-Color, streak, luster, hardness, specific gravity, crystal habit/form,
fracture, and cleavage
• Mineral classes and silicates
-Mineral classes, most importantly silicates
-Silica tetrahedra building block
-Silicate types: from individual tetrahedra to framework Chapter 5 5
Chapter

39. Mineral Classes
• Minerals are classified by their dominant anion.
Silicates SiO24- Most rock-forming mins!
• Oxides O2- Magnetite, Hematite
• Sulfides S- Pyrite, Galena
• Sulfates SO42- Gypsum
• Halides Cl- or F- Fluorite, Halite
• Carbonates CO32- Calcite, Dolomite
• Native Elements Cu, Au, C Copper, Gold, Graphite
Malachite (Carbonate) Fluorite (Halide) Native Copper
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40. Silicate Minerals
• Silicates are known as the rock-forming minerals.
• They dominate the Earth’s crust.
• Oxygen and silicon…
• -94.7% of crustal volume
• -74.3% of crustal mass
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41. Silicate Minerals
• The building block (anion) unit is the silica tetrahedron.
• 4 oxygen atoms are bonded to 1 silicon atom (SiO44-).
• -silicon is tiny; oxygen is huge
• -the silica tetrahedron has a net -4 ionic charge
• -the silicate unit can be depicted by…
• -spheres
• -ball and stick model
• -polyhedra
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42. Silicate Minerals
• Silica tetrahedra link together by sharing oxygens.
• More shared oxygen  higher Si:O ratio; governs…
• -melting temp
• -mineral structure and cations present
• -susceptibility to chemical weathering
Type of Silicate Structure Formula Si:O Ratio
Independent Tetrahedra SiO4 0.25
Double Tetrahedra Si2O7 0.29
Ring Silicates Si6O18 0.33
Single Chains SiO3 0.33
Double Chains Si4O11 0.36
Sheet Silicates Si2O5 0.40
Framework Silicates SiO2 0.50
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43. Independent Tetrahedra
• Tetrahedra share no oxygens - linked by cations.
• Olivine Group.
• High temperature Fe-Mg silicate.
• Small green crystals; no cleavage.
• Garnet Group.
• Equant crystals with no cleavage.
• Dodecahedral (12 sided) crystals.
Garnet
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44. Single-Chain Silicates
• Single-chain structures bonded with Fe and Mg.
• Pyroxene Group.
• Black to green color.
• Two distinctive cleavages at nearly 90°.
• Stubby crystals.
• Augite is the most common pyroxene.
Pyroxene
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45. Double-Chain Silicates
• Double chain of silica tetrahedra bonded together.
• Contain a variety of cations.
• Amphiboles – two perfect cleavages
• Elongate crystals
Hornblende
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46. Sheet Silicates
• 2-dimensional sheets of linked tetrahedra.
• Characterized by one direction of perfect cleavage.
• Mica Group – botite (dark) and mucsovite (light)
Clay Mineral Group – feldspar weathering residue; tiny
Muscovite (Mica)
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47. Framework Silicates
• All 4 oxygens in the silica tetrahedra are shared.
• Feldspar Group – plagioclase and potassium feldspar
• Silica (Quartz) Group – contains only si and o
Potassium Feldspar
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