3 rocks including_metamorphic_rocks

CE-312
Engineering Geology and Seismology
Lecture-3
Rocks
Instructor:
Dr. Shahid Ullah
Earthquake Engineering Center
Department of Civil Engineering, UET Peshawar.

Contents of the Lecture
 What are rocks?
 Classification of rocks
 Classification of Igneous rocks
 Classification of sedimentary rocks
 Classification of metamorphic rocks
2

What are rocks?
 Rock is defined as:
• Naturally occurring solid aggregate of minerals and or non-
minerals (organic substance, and
• does not have a specific chemical composition.
 The properties and nature of rocks are determined by:
• As the basic constituent of rock, minerals control much of
rock behavior. Some minerals are very strong and resistant
to deterioration and produce rock with similar properties,
while others are much softer and produce weaker rock.
• The manner in which minerals are arranged relative to each
other i.e. The texture of the rock.
• *texture is the size, shape and arrangement of mineral grain in a
rock.
3

Classification of rocks
 Based on their formation, the rocks have been
classified into three main types:
 Igneous rocks:
• The rocks which are formed by cooling and solidification
of magma.
 Sedimentary rocks:
• The rocks which are formed by consolidation and
cementation of the sediments deposited, mostly, under
water.
 Metamorphic rocks:
• The rock which are formed when the pre-existing rocks
have been changed in texture and composition by increased
temperature and pressure.
4

Igneous rocks
 Magma is a hot viscous solution of silicates and non-
silicates minerals, containing gases.
• When magma comes out upon on the earth‘s surface, is called
lava.
 Based on the composition, two types of magma:
 Acid magma: It is rich in Si, Na, K and poor in Ca, Mg and Fe.
Acid igneous rocks are light in color, low in specific gravity
(2.7) , and have high proportion of minerals like Quartz,
Feldspars and some mica. e.g. Granite.
 Basic magma: It is rich in Ca, Mg and Fe and poor in Si, Na and
K. Basic igneous rocks are dark in color (often black) ,relatively
high in specific gravity (3.2) , and are rich in minerals like
augite, hornblende, plagioclase and iron ore. e.g. Basalt.
5

Igneous rocks
6
Basalt
rock
Granite rock
Granite
rock

Igneous rocks
 Based on silica content, igneous
rocks can be classified as:
a) Ultra basic rocks: contains less
than 45% silica e.g. Peridotite.
b) Basic rocks: contains silica
between 45% and 55 % e.g.
Basalt.
c) Intermediate rocks: contains
silica between 55% and 65% .
e.g. Diorite.
d) Acid rocks: contains more than
65% silica. e.g. Granite.
7
Diorite

Texture of igneous rocks
 Texture means the size, shape and arrangement of
mineral grains in a rock.
 Texture is controlled by the cooling rate of magma.
• Slower the cooling rate: coarser is the grain of rock
• Rapid cooling rate: leads to glassy texture (non-crystalline)
• Between these two extremes are fine grained and
cryptocrystalline texture.
 Phaneritic: Igneous rocks whose constituent
mineral grains can be seen with the nacked eyes.
 Aphanitic: Otherwise
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 Types of Texture:
• Holocrystalline: if the rock is made up entirely of crystalline
material (100% crystals)
• Coarse grained: if the average grains or crystals of the
minerals are more than 5 mm in diamete.
• Fine grained: like granulated sugar, if the average diameter is
less than 1 mm.
• Cryptocrystalline: if the crystals are invisble to the nacked
eyes, and visible only under the microscope.
• Glassy: no crystallization. Magma is consolidated as an
amorphus mass.
• Porphyritic: when large and small crystals are both present in
the same rock. Due to cooling of magma in two or more
stages.
• Vesicular: glassy volcanic rock which contain gas cavities,
called Visicles.
9
Texture of igneous rocks

• Classification of igneous rocks based on texture and
mode of occurrence:
1) Plutonic (intrusive) rocks: are formed when magma
cools slowly and crystallize at great depth. Leading to
coarse grained texture. e.g. Granite.
2) Volcanic (extrusive) rocks: are formed when the
magma erupts at the earth‘s surface and cools rapidly.
Leading to fine grained or glassy texture. e.g. Basalt.
3) Hypabyssal rocks: are formed due to injection of
igneous bodies near to the earth‘s surface. (at depths in
between plutonic and volcanic). examples of such
igneous bodies are Dykes and sills. Leading to fine
grained, porphyritic or partly glassy texture. e.g. Granite
porphyry, dolerite.
10
Igneous rocks

Igneous bodies
Dyke: A dyke is vertical wall-like igneous body that cuts across the
bedding of the rock. The thickness of the dyke may vary from a few
centimeters to a hundred meter or more. Dyke actually represents a
crustal fracture into which the magma was injected. Dyke is always
younger than the rocks that contain it.
11
Sill: A sill is a sheet like
igneous body which vary in
thickness from a few
centimeter to several hundred
meters. The sill is parallel to
the bedding of rock and may
be horizontal, inclined or
vertical depending upon the
strata. The sill does not cut
across preexisting rocks, in
contrast to dikes, which do cut
across older rocks.

Common igenous rocks
Granite: is coarse grained, an intrusive rock. It is the most
common and familiar igneous rocks. Granite contains
primarily orthoclase feldspar and quartz, with some biotite
and amphibole. The average granite contains 60% felsdpars,
30% quartz and 10% ferromagnesian minerals. It is mostly
light in color with a white or pink tint according to the color
of the feldspar.
 Engineering properties: It as an excellent frost
resistance. Because of the minerals composition and
interlocking of crystals, granite is hard and abrasion
resistant. The compressive strength of granite is on
average 24,500 psi. Granite can be used to support any
load of ordinary structures.
12

Diorite: is coarse grained, an intrusive rock. It is mainly
composed of plagioclase feldspar (more than 50 %) and
hornblends. However, in some varieties augite and biotite
may be present. Most diorites contain little or no quartz. It is
less abundant than granite.
 Diorite is a relatively rare rock.
 Diorite has been used for crushed stone for monumental
and decorative purposes than for structural purposes.
 Diorite is an extremely hard rock, making it difficult to
carve and work with. It is so hard that ancient
civilizations (such as Ancient Egypt) used diorite balls to
work granite. Its hardness, however, also allows it to be
worked finely and take a high polish, and to provide a
durable finished work
13

14
Diorite Porphyry vase from
predynastic Ancient Egypt, ca.
3600 BC; approx 30 cm.

Pumice: rocks are igneous rocks which were formed
when lava cooled quickly above ground. You can see
where little pockets of air had been. This rock is so
light, that many pumice rocks will actually float in
water. It is formed on the surface of acid lavas. Because
this rock is so light, it is used quite often as a decorative
landscape stone. Ground to a powder, it is used as an
abrasive in polish compounds and in Lava soap.
15
A 10 centimeter (6 -
inch) piece of pumice
supported by a rolled
- up U.S. 20-dollar
bill demonstrates its
very low density.

 Pumice is widely used to make lightweight concrete or
insulative low-density breeze blocks. When used as an
additive for cement, a fine-grained version of pumice
called pozzolan is mixed with lime to form a light-
weight, smooth, plaster-like concrete. This form of
concrete was used as far back as Roman times. Roman
engineers used it to build the huge dome of the Pantheon
and as construction material for many aqueducts.
 It is also used as an abrasive, especially in polishes, pencil
erasers, cosmetic exfoliants, and the production of stone-
washed jeans. "Pumice stones" are often used in beauty
salons during the pedicure process to remove dry and
excess skin from the bottom of the foot as well as
calluses. It was also used in ancient Greek and Roman
times to remove excess hair.
16

Basalt: is a dense looking black extrusive
(volcanic) rock that makes up most of the world's
oceanic crust, produced from upwelling mantle
below ocean ridges.
 Its texture is fine-grained to glassy, so that the
individual minerals are not visible, but they
include pyroxene, plagioclase feldspar and
olivine. These minerals are visible in the coarse-
grained, plutonic version of basalt called Gabbro.
 Basalt is used in construction (e.g. as building
blocks or in the groundwork), making
cobblestones (from columnar basalt) and in
making statues. Heating and extruding basalt
yields stone wool, an excellent thermal insulator.
17

Syenite: It is a coarse grain rock, mainly
composed of orthoclase (Alkaili feldspar) ,
soda-plagioclase and one or more mafic
minerals such as biotite and hornblende. It
has little or no quartz. Color is variable but
are generally light in color.
 The general properties of Syenite are
similar to granite. Its rare compared to
granite. It is used as dimension stone for
building facings, foyers etc (often
preferred to granite due to its better fire-
resistant qualities); can be used as
aggregate in the building and roads.
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Engineering Properties of Some Un-weathered Igneous Rocks
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Engineering Considerations of Igneous Rocks
 Fine-grained igneous rocks cannot be used as aggregates
in Portland cement due to volume expansion caused by
the Alkali-silica reaction. Solutions include:
(a) Can be used in low alkali cement;
(b) Non-reactive aggregates go with the high alkali cement;
(c) Add pozzolans, coal-ashes, etc. in the aggregate-cement mixture
to minimize the reaction.
 Fine-grained igneous rocks (e.g., basalt) are good for
aggregates (e.g., basalt) as paving aggregates goes with
asphalt.
 Siting of foundations needs to avoid weathered rocks
(e.g., dams, bridge piers, etc.);
 Igneous rocks are good for dimension stone (tombstone
etc.) because their resistance to weathering but one need
to avoid fractures.
20

Sedimentary rocks
The rocks which are formed by consolidation and
cementation of the sediments deposited, mostly, under water.
 Sediment is the collective name for loose, solid particles
that originate from:
1) Weathering and erosion of preexisting rocks (Clastic)
2) Chemical precipitation from solution, including secretion by
organisms in water (Non Clastic)
 These sediments are transported by water and gets
deposited in suitable depression of the earth, where it gets
consolidated and cemented to form sedimentary rocks.
 Sedimentary rocks occur in layers, and frequently contain
fossils.
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Sedimentary rocks
• Particle size in sediments: the constituent particles
of sediments may be classified into gravel and pebble,
sand, silt, and clay, and each of these give rise to a
particular type of rock.
22
Grade Grain size Rock type
Gravel or pebble 2 mm and above Conglomerate
Sand 0.1 mm to 2 mm Sand stone
Silt 0.01 mm to 0.1 mm Silt stone
Mud or clay Less than 0.01 mm Mudstone, shale

Classification of Sedimentary rocks
• On the basis of formation/types of sediments,
sedimentrary rocks (SR) are classified into 3 types.
1) Mechanical (Clastic) SR: Consisting of sediments
material (gravel, sand, silt and clay) formed from
mechanical weathering of rocks.
 Examples are: Breccia, conglomerate, sandstone,siltstone
and shales.
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Chert Breccia Limestone Breccia Conglomerate

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Sandstone
Siltstone
Shale

2) Organic SR: consisting of accumulated animal or
plant debries/remains.
 Examples are: coal, some dolomites and some limestones.
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Bitumen coal Dolomite rock Black limestone

3) Chemical SR: formed due to precipation and
accumulation of soluble constituents.
Examples are: rock salt, iron ore, flint, chert etc.
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Rock salt
(halite)
Iron ore (Oolithic
hematite)
Flint knife Chert SiO2

Consolidation/lithification
It is the process by which soft and loose sediments are converted into
hard and firm rocks. Mainly three methods:
1) Compaction or dehydration: when a bed is burried under more
sediments, it gets consolidated due to the pressure of the overlying
mass. The excess of water is squeezed out and the cohesion is
developed between the grain of sediments. Fine grained sediments
(e.g clays) are consolidated by this process.
2) Cementation: coarse grained sediments (e.g gravel and pebbles)
are mostly consolidated by cementation. These being porous, water
circulates through them and dissolved mineral matter may be
precipitated between the grains, thereby causing cementation. The
most common cementing materials are silica, calcium carbonate,
iron oxides and clay minerals. E.g. Congolomerates.
3) Crystallization: consolidation is caused by the crystallization of
constituent sediments. E.g. Limestone, dolomites, salt ,gypsum etc.
27

Structural features of sedimentary rocks
Sedimentary structures are are visible features within
sedimentary rocks. They are formed during sediment
deposition. The study of these structure reveals about
their origin, and helps in determining thier age. The
main sedimentary structures are:
 Stratification
 Lamination
 Corss-bedding
 Graded-bedding
 Mud cracks
 concretions
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Stratification
 The deposition of sediments into layers or beds is called
stratification. This is one of the most commonly observed
sedimentary structure.
 Bed: is a layer of sediments, whose thickness is greater than 1
cm.
 The planes dividing different beds are called bedding planes.
 Following are the reasons for the formation of stratification:
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i. Difference in the kind of materials
deposited, e.g. Shale and limestone beds.
ii. Difference in the size of particles
deposited, e.g. Coarse grained and fine
grained sediments
iii. Difference in the color of material
deposited, e.g. Light grey and dark grey
layers of limestone. Dushanbe, Tajikistan

Lamination and Cross bedding
30
Lamination: layers of sediments whose
thickness is less than 1 cm. These deposits are
typically formed by fine grained sediments such
as silts and clays and often represents seasonal
deposition. It is often found in fine grained
sedimentary rocks like shales.
Shale
Sandstone deposited by river Sanddune deposited by wind
Cross bedding: it is also called current bedding or false bedding.
These are the minor bedding or laminations which lie at an angle
to the planes of general stratification. This structure is found in
shallow water and wind formed deposits

Graded bedding and ripple marks
Graded bedding: When a sedimentary bed shows a gradation in
grain size, from coarse below to a fine grain above, is called
graded bedding.
31
Ripple marks: are the wavy undulations
which are seen on the surface of some
sedimentary rocks. These are produced by
the action of waves and currents in shallow
water, and also by the action of wind. They
are on small scale compared to cross-
bedding. They are of two types:
1) Asymmetrical or current ripple marks: they
can give an indication of wave
direction(both water and wind).
2) Symmetrical or oscillation ripple marks: are
formed when water moves back and forth,
in steady water environment, like tidal.

Mud cracks and concretion
Mud cracks are formed from the drying out of wet
sediment at the surface of the Earth. The cracks
form due to shrinkage of the sediment as it dries.
The presence of mud cracks indicates that the
sediment was exposed at the surface shortly after
deposition, since drying of the sediment would not
occur beneath a body of water.
32
Concretion is a hard, compact mass of
matter formed by the perecipitation of
mineral cement within the spaces between
particles in a sedimentary rock. Their
shape may be round, elliptical, oval or
irregular. It generally consists of calcium
carbonate, or silica and often possess an
internal radiating or concentric structure.
Concretions in Kazakhstan
Ancient mud cracks

Conglomerate: coarse grained clastic sedimentary rock, produced by
consolidation and cementation of rounded pebbles and gravels. The
pores are filled with a matrix of fine sands, rock particles and some
cementing materials.
 It can contain clasts of any rock material or weathering product that
is washed downstream or down current. The rounded clasts of
conglomerate can be mineral particles such as quartz, or they can be
sedimentary, metamorphic, or igneous rock fragments.
 It has very few commercial use. Its variable composition makes it a
rock of unreliable physical strength and durability. Its inability to
break cleanly makes it a poor candidate for dimension stone.
Conglomerate can be crushed to make a fine aggregate that can be
used where a low-performance material is suitable.
 Its analysis can be prospecting tool. For example, most diamond
deposits are hosted in kimberlite. If a conglomerate contains clasts
of kimberlite, then the source of that kimberlite must be somewhere
upstream.
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Description of common Sedimentary rocks

Conglomerate:
34
This image of martian conglomerate was
acquired by NASA's Curiosity rover on the
surface of Mars. It shows an outcrop of
conglomerate and some pebble-size
weathering debris. The round pebbles are too
large to have been moved and shaped by
wind, thus they had to have been transported a
significant distance by water. This photo from
September 2012 was the strongest evidence of
the existence of water on Mars that had been
obtained at that time
Martian conglomerate

Breccia: It resembles conglomerates, but have angular
fragments instead of rounded pebbles.
 Because the grains are rounded so rapidly during
transport, it is unlikely that the angular fragments
within breccia have moved very far from their source.
 It might have formed from fragments that have
accumulated at the base of a steep slope of rock (i.e.
landslide) that is being mechanically weathered.
35
Debris Flow Breccia: Outcrop of a breccia
thought to have formed from debris flow deposits
in Death Valley National Park. The largest clasts
are about three feet (one meter) across and are
thought to be from the Noonday Dolomite. United
States Geological Survey image.

Sandstone: is mainly composed of sand size grains of
quartz which are cemented together. The cementing
materials may be silicate, calcite, iron-oxide or clay.
 It is often mined for use as a construction material or
as a raw material used in manufacturing. In the
subsurface, sandstone often serves as an aquifer for
groundwater or as a reservoir for oil and natural gas.
 Used in Cement Manufacture, Construction
Aggregate, for Road Aggregate, Production of Glass
and Ceramics, Raw material for the manufacture of
mortar.
36

Shale: it is laminated fine grained clastic sedimentary rock.
Mainly composed of clay minerals, some silt size grains of
quartz.
 Shales are often soft and can be scratched by a knife.
 Shale is fissile and laminated. "Laminated" means that the
rock is made up of many thin layers. "Fissile" means that
the rock readily splits into thin pieces along the
laminations.
 Black shales contain organic material that sometimes
breaks down to form natural gas or oil. Other shales can
be crushed and mixed with water to produce clays that
can be made into a variety of useful objects.
 Used in Cement Manufacture, Construction Aggregate,
for Road Aggregate, Making natural cement, Raw
material for the manufacture of mortar
37

Mudstone: Unlaminated clayey rocks are called mudstones.
Limestone: mainly consists of calcite. Some limestones may also
contain calcarious shells of marine organisms.
 Limestones are fine grained, and are identified by their
softness, their fossil content, and their effervescence in dilute
hydrochloric acid.
 It most commonly forms in clear, warm, shallow marine
waters. It is usually an organic sedimentary rock that forms
from the accumulation of shell, coral, alga, and fecal debris. It
can also be a chemical sedimentary rock formed by the
precipitation of calcium carbonate from lake or ocean water.
 Limestones are the primary source of lime for cements. It is
fired in a kiln with crushed shale to make cement. Limestone
can be crushed and used as road ballast. It is used as an
aggregate in concrete.
38

Marl: Impure limestones which contain mixture of clay
and calcarious matter, are known as marls.
Dolomite: is a magnesian limestone which is composed
of double carbonate of calcium and magnesium
[CaMg(Co3)2].
 Distinguished from ordinary limestone by its higher
hardness, greater specific gravity, and inferior
solubility in hydrochloric acid.
 Used as Dimension Stone, Cement Manufacture, for
Road Aggregate, Making natural cement,
Manufacture of Magnesium and Dolomite
Refractories, Production of Glass and Ceramics,
Serves as an Oil and Gas Reservoir rock
39

Engineering Properties of Some Un-weathered Sedimentary Rocks
40

Metamorphic rocks
• Metamorphic rocks are formed when the pre-existing
rocks (igneous or sedimentary) are subjected to
increased temperature, pressure and action of
chemically active fluids.
 During metamorphism, recrystallization of the
mineral constituents take place which results in the
production of new minerals and textures.
 Metamorphism means "change in form".
 Generally the metamorphic processes improve the
engineering behavior of these rocks by increasing
their hardness and strength. Nevertheless, some
metamorphic rocks still can be problematic.
41

The agents which bring about metamorphism of rocks are:
1) Physical agents: Heat, Uniform pressure (or confining or
hydrostatic), and directed pressure (stress).
2) Chemical agents: chemically active water and gases.
 These agents produce changes in the pre-existing rocks,
that are either physical, chemical or both.
 Physical changes produces new textue whereas
chemical changes produce new minerals.
 Recrystallization is the process which produces new
texture. In this process, the original mineral undergo a
change in their structure i.e. They are flattened or
elongate.
42
Agents of Metamorphism or factors controlling
metamorphism

Depending upon the dominance of one or the other of
the agents, the metamorphism is classified as:
1) Thermal metamorphism. Here the changes brough
in rocks are mainly due to heat, but heated magmatic
water or vapors carrying mineral matter in solution
also play important part. The confining pressure is
usually relatively low because it mostly takes place
not too far beneath Earth’s surface (<10Km).
 When thermal metamorphism occurs in the
immediate vicinity of igneous intrusions, it is called
contact metamorphism. and when it occurs on a
regional scale (large scale) at depth, it is called
plutonic metamorphism.
43
Types of Metamorphism

 Uniform pressure predominates in thermal
metamorphism, thus leading to the development of dense
and equidimensional minerals during recrystallization.
And the resulting rocks are non-foliated* having even
grained texture.
 Foliation*: referes to the repetitive layers in metamorphic
rocks, whose thickness varies from a few mm to over a
meter. They are caused by shearing forces or differential
pressure.
 During contact metamorphism, clays and shales may
changed into the very fine-grained Porcellanite, hornfelse
or even mica-schist, while sandstones and limestones may
form quartzites and marbles, respectively.
44

2) Regional or dynamothermal metamorphism. It is
caused when both directed pressure and heat act
together.
 The directed pressure involves movement and shearing,
and therefore it is the main factor in forming foliated and
cleavable rocks. The new minerals developed under
directed pressure are usually flat, tabular, elongated, or
bladed in nature, e.g. Muscovite,biotite, chlorite, talc etc.
These minerals develop with their flat sides at right
angles to the direction of pressure.
 The foliated rocks include slates, phyllites, schists, gneiss
etc.
 This metamorphism is associated with folded mountain
ranges.
45

3) Cataclastic metamorphism. Here mainly the directed
pressure or stress predominates. The stress produces
shearing movements in the rocks and causes crushing,
granulation and powdering. Therefore, cataclastic rocks
show mainly mechanical breaking with little new
mineral formation.
 This takes place near the earth surface, where rocks are
hard and brittle.
 Example of cataclastic rocks are mylonites and fault
breccia.
46

4) Metasomatism. The metasomatic replacements of
rocks are brought about by deposition from
hydrothermal solution (hot magmatic water).
 Th replacement takes place molecule by molecule, so
that the new mineral is added, the old is removed.
 The metasomatic replacement is commonly
associated with carbonate rocks such as limestones
and dolomites, which are easily dissolved and
replaced by silica, iron ore etc.
47

48
Common Metamorphic Transformations

Metamorphic zones
The degree or intensity of metamorphism generally increases
with depth becasue as the depth increases, temperature and
pressue also increases. From the earth surface downward there
are three zones of metamorphism.
1) Epizone: this zone lies near the earth surface where
temperature is upto 3000C, and directed pressure is high.
Clastic metamorphism takes place here. The alteration in
rock is weak. The typical rocks are phyllites.
2) Mesozone: an intermediate zone, where temperature is
between 3000C and 5000C, and directed pressure is also high.
Dynamothermal metamorphism takes place here. Schists are
the typical rocks of this zone.
3) Ketazone: the bottom most zone, where directed pressure is
absent, uniform pressure is high, and temp is above 5000C.
Plutonic metamorphism predominates here to produce even
grained rocks.
49

Grade of metamorphism
 It varies directly with the amount of heat and pressure to which
the rock is subjected.
 As the degree of metamorphism increases, new minerals
become stable and crystallize. The minerals present in a
metamorphic rocks are thus indicators of the P/T conditions at
the time of the last recrystallization. Metamorphic Grade is a
scale of metamorphic intensity which uses indicator
minerals as geothermometers and geobarometers.
 Slate and phyllite which show a low grade of metamorphism,
are formed away from the intrusive igneous body, while high
grade metamorphic rock like gneiss is formed near its margin.
 Higher the grade of metamorphism, higher the grain size, e.g.
Slates and phyllites are fine grained, while schists and gneiss
are coarse grained.
50

• In general, proceeding from low grade (lower
pressure and temperature) to high grade (higher
pressure and temperature), the following facies are
recognized:
51
Zeolite: low temperature, low pressure
Prehnite-pumpellyite: low temperature,
low-medium pressure
Greenschist: low-medium temperature,
low-medium pressure
Blueschist: low-medium temperature,
high pressure
Amphibolite: medium-high temperature,
medium-high pressure
Granulite: high temperature, high
pressure
Grade of metamorphism

Slate: Slates are produced by the low grade
regionale metamorphism of shales.
 They are foliated and fine grained rocks.
 They are composed of very fine grained
mixture of quartz, chlorite, muscovite and
feldspars.
52
Common metamorphic rocks
 It is popular for a wide variety of uses such
as roofing, flooring, and flagging because of
its durability and attractive appearance.

Phyllite: is a foliated, low grade metamorphic rock,
having glossy and shinning lustre. This luster is due to
the presence of large amount of fine flakes of mica
(muscovite).
 Composed of mainly muscovite and quartz.
 It is intermediate grade between slate and schist.
53

Schist: Schist is a foliated metamorphic rock made up of plate-
shaped mineral grains that are large enough to see with an
unaided eye.
 It usually forms on a continental side of a convergent plate
boundary where sedimentary rocks, such as shales and
mudstones, have been subjected to compressive forces, heat,
and chemical activity.
54
They are largely composed of flaky minerals
such as muscovite, biotite, hornblende,
chloride, talc etc.
Depending upon the type of flaky mineral
present, they are named as muscovite-schist,
biotite-schist, hornblende-schist,etc.
 Because of its lower strenght, it is
unsuitable for use as construction
aggregate,or building stone.
The dominant visible mineral in
this schist is muscovite.

Gneiss: is a high graded, coarse grained, foliated metamorphic
rock.
 It has a banded appearance and is made up of granular mineral
grains .
 It is composed of feldspars, quartz and some mafic minerals.
 Are distinguished by the minerals present in large amount, e.g.
Biotite-gneiss, hornblende-gneiss etc.
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 Because of its strength, it is used as construction
aggregates in road construction, building site
preparation, and landscaping projects.
 Some gneiss is durable enough to perform well as a
dimension stone. These rocks are sawn or sheared
into blocks and slabs used in a variety of building,
paving, and curbing projects.

Marble: Marble is a metamorphic rock that forms when
limestone is subjected to the heat and pressure of
metamorphism. It is composed primarily of the mineral
calcite (CaCO3) and usually contains other minerals,
such as clay minerals, micas, quartz, pyrite, iron oxides,
and graphite.
 Most marble forms at convergent plate boundaries
where large areas of Earth's crust are exposed to
regional metamorphism. Some marble also forms by
contact metamorphism when a hot magma body
heats adjacent limestone.
 It has a hardness of 3 on Mohs scale, which makes it
easy to carve for sculptures and ornamental objects.
 Marble is used as an aggregates in highways,
railroad beds, building foundation , and as a
dimension stone.
 It is also used for acid neutralization in chemical
industry.
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Pink marble
Gray marble

Engineering Properties of Some Common Metamorphic Rocks
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The rock cycle
 The rock cycle is a fundamental concept in geology that
describes the dynamic transitions through geologic time among
the three main rock types: sedimentary, metamorphic,
and igneous. As the diagram illustrates, each of the types of
rocks are altered or destroyed when it is forced out of its
equilibrium conditions.
 An igneous rock such as basalt may break down and dissolve
when exposed to the atmosphere, or melt as it
is subducted under a continent. Due to the driving forces of the
rock cycle, plate tectonics and the water cycle, rocks do not
remain in equilibrium and are forced to change as they
encounter new environments.
 The rock cycle is an illustration that explains how the three rock
types are related to each other, and how processes change
from one type to another over time.
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The rock cycle
Note: All rocks may not go through each step in the cycle e.g. sedimentary
rocks might be uplifted and exposed to weathering, creating new sediment.

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