IT IS BEST NOTE

1. Engineering Geology for Civil Engineers
CEng 4309
Belay Birhanu (MSc.)
belaybelete27@gmail.com
Office Block 520/12
Chapter 2
Crystals, Minerals and Rocks

2. Recap
Chapter one
✓Geology and Branches of Geology
✓Origin and History of the Earth
✓ Internal structure and composition of the Earth
✓Earth’s Continental Plate Movement
✓Rock Age Determination Techniques
✓Application of Engineering Geology
2

3. Learning Objective
After complete this chapter the student able to:-
•To understand the concept of mineral and rock
•To understand the different types of minerals and rocks
•To understand the engineering geology consideration of
rocks
3

4. Today Agenda
• Concept of Crystals
• Minerals, formation of minerals, properties of minerals
and types of minerals
4

5. Crystals, Minerals and Rocks
➢All Earth materials are composed of atoms bound together.
➢ Minerals are composed of atoms bonded together and are
the building blocks of rocks.
➢ Rocks are composed of minerals and they record various
geologic processes.
➢Matter can exist in three states:-Liquid, Gas and solid
•Solid:- solid molecules can be crystalline solids and non
crystalline solids (Amorphous)
5

6. Non crystalline (Amorphous) Solid
➢ Any solid having random internal arrangement of its
constituent atoms and ions with no external crystal
structure. E.g. Graphite
Crystalline Solid :-
➢ Any solid having a regular internal arrangement of
atoms, ions in three dimensional array in a regular and
repeating manner. E.g. diamond
➢Graphite and diamond both are made up of the same
element carbon, but graphite is amorphous (the carbon
atoms are distributed randomly) and diamond is crystalline
solid (the atoms are arranged regularly)
6

7. What is crystal?
➢ A Crystal is a solid piece having homogeneous physical
and chemical composition, externally shaped by
symmetrically natural smooth faces.
➢Crystal have highly ordered atomic arrangement which
means that the atoms in a mineral are arranged in an
ordered geometric pattern. This ordered arrangement of
atoms is called a crystal structure, and thus all minerals are
crystals.
➢ Each mineral has a crystal structure that will always be
found for that mineral, i.e. every crystal of quartz will have
the same ordered internal arrangement of atoms. 7

8. 8
To Geologists
➢ Minerals are naturally occurring inorganic solid that has
specific chemical composition and regular internal crystal
structure.
➢ Therefore, minerals are:
o Naturally occurring: found in nature or produced by
geological process.
o Inorganic: excluded the organic mater that make up
plants and animals. do not contain hydro carbons with
carbon-hydrogen bonds and Not produced by biological
processes
What is Mineral ?

9. 9
o Solid: Neither liquid nor gas are minerals
o Has specific (definite) chemical composition: a mineral
have unique chemical composition with a specific
(unique) chemical formula
o Has regular internal structure: Arrangement of
atoms in regular, repeating patterns…… with
disordered arrangements are not minerals
What is Mineral ?

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Some remarks and exceptions to the definition of minerals
➢Most of the minerals are compounds of two or
more elements, but there are few minerals such as,
Sulphur, diamond, Au which are made up of single
elements, called Native minerals
➢Hg is a mineral but not solid
➢Even though coal and petroleum are natural
occurring they are not minerals, because they are
organic in origin

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How Minerals form?
➢ Minerals form via natural environmental processes that
cause atoms to bond together to form solids. These include:
1) Precipitation from solution: Solutions from which minerals
precipitate include:
• Surface water & Groundwater
• Hydrothermal solutions, which are warm, aqueous solutions
that have been heated at depth and/or by proximity to a
body of magma.
2) Sublimation from a gas
➢ Sublimation occurs where volcanic gases are vented at
Earth’s surface or where gas phases separate from solution
in the subsurface.
➢ Lava flows at the surface which form volcanic and Magma bodies in
the subsurface, which form plutonic minerals and rocks.

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3) Solid state growth
➢ In solid state growth, new mineral crystals grow from the
constituents of pre-existing minerals. This is especially
common during the formation of metamorphic minerals and
rocks.
4) Solid – liquid or solid – gas reactions
➢ Insuch reactions, atoms are exchanged between the solid
minerals and the liquid or gas phase with which they are in
contact, producing a new mineral.
➢ These solid – liquid or solid – gas reactions are common in
mineral - forming processes that range from weathering
through vein formation to metamorphism.

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Properties of Minerals
➢ The properties (i.e. physical, chemical or optical properties) of
minerals are the traits which are used to identify and description of
mineral species.
➢ These traits include color, streak, luster, density, hardness,
cleavage, fracture, tenacity, and crystal habit.
1. Color
2. Luster
3. Hardness
4. Crystal shape
5. Cleavage
6. Streak
7. Fracture
8. Transparency
9. Specific gravity and others
Physical properties of minerals

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➢ Generally unreliable for mineral identification
➢ Often highly variable due to slight changes in mineral chemistry
➢ Exotic colorations of certain minerals produce gemstones
➢ Quartz (SiO2) exhibits
a variety of colors
o Sulfur - Yellow
o Azurite - Blue
o Malachite - Green
o Cinnabar - Red
o Chromite - Black
A) Color

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B) Streak
➢ Color of a mineral in its powdered form
➢ Streak is obtained on an unglazed porcelain plate

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▪ Resistance of a mineral
to the abrasion or
scratching.
▪ All the minerals are
compared to a standard
scale called the Mohs
scale of hardness.
▪ Moh’s scale relates the
hardness of minerals with
some common objects, such
as fingernails, copper
pennies, a steel knife blade,
and glass.
C) Hardness

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✓ External expression of a mineral’s internal structure
✓ Often interrupted due to competition for space and rapid
loss of heat
Cubic crystals of
pyrite
D) Crystal Form

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E) Luster
➢ It is the quality and intensity of light reflected from the
surface of a minerals (response to light).
➢ Two minerals can have the same color but different luster.
➢ Luster depends on the crystal structure of minerals
➢ There are two major type of luster
Galena, metallic luster Orthoclase, non metallic luster
1) Metallic Luster 2) Non-metallic Luster

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2.1.2 Types of minerals
A. Based on their economic importance
1. Economic minerals: those explored for their
economic importance
2. Rock forming minerals: constituents of rocks.
B. Based on their origins
1. Primary Minerals: directly crystallize from
cooling magma
2. Secondary Minerals: formed after sedimentation
and metamorphism

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C. Based on their importance to the naming of rocks
1. Essential minerals: their present or absent is affect
naming of the rock e.g. quartz, feldspars for granite
2. Accessory Minerals (non-essential): their present or
absence don’t affect the naming of the rocks. E.g. Zircon
in granite.
D. Based on their chemical composition:
•Silicate,
•Native,
•Oxides, etc.

21. Summary
• A crystal is a solid whose atoms are arranged in a "highly
ordered" repeating pattern.
• Minerals are naturally occurring inorganic solid that has specific
chemical composition and regular internal crystal structure.
• Minerals form via natural environmental processes These
include:- Precipitation from solution, Sublimation from a gas,
Solid state growth and Solid – liquid or solid – gas reactions
• Properties of minerals is used to identify the minerals and some
Physical properties of minerals include:-Color, Luster, Hardness,
Crystal shape, Streak and others
• Mineral can be classified based on economic importance, origin,
and their importance to the naming of rocks
21

22. Thank you
22

23. Chemical Classification of Minerals (Groups of
Minerals
23
Belay Birhanu (MSc.)
belaybelete27@gmail.com
Office Block 520/12
Chapter 2
Crystals, Minerals and Rocks

24. Recap
✓What is crystal?
✓What minerals?
✓Formation of minerals and properties of minerals
✓Different types of minerals based on economic importance,
origin, and their importance to the naming of rocks
24

25. Today Agenda
•Chemical Classification of Minerals (Groups of Minerals)
•Rock forming minerals
25

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Chemical Classification of Minerals (Groups of Minerals)
➢ Mineral are classified on the bases of their chemical
composition, and the most common once are the
following:
CHEMICAL
FORMULA
MINERAL
CHEMICAL GROUP
Au
Gold
Metallic
minerals
(I)
NATIVE
MINERALS
Ag
Silver
P
Platinum
Cu
Copper
S
Sulphur
Non-Metallic
Minerals C
Diamond

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CHEMICAL
FORMULA
MINERAL
CHEMICAL GROUP
Fe2O3
Hematite
OXIDES
(2)
OXIDES
AND
HYDROXIDES
Fe3O4
Magnetite
FeTiO3
Ilmenite
Al2O3
Corundum
FeCr2O4
Chromite
TiO2
Rutile
UO2
Uranenite
MnO2
Pyrolusite
Fe2O3. 2H2O
Limonite
HYDROXIDES
MnO2.nH2O
Psilomelane
Mn2O3.H2O
Manganite
Fe2O3.nH2O
Goethite

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CHEMICAL
FORMULA
MINERAL
CHEMICAL GROUP
pbS
Galena
(5)
SULPHIDES
HgS
Cinnabar
FeS2
Pyrite
CuFeS2
Chalcopyrite
ZnS
Sphalerite
NaCl
Halite
(6)
HALIDES
KCl
Sylvite
CaF2
Fluorite
Na3AlF6
Kryolite

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CHEMICAL
FORMULA
MINERAL
CHEMICAL GROUP
(Fe,Mn)WO4
Wolframite
(7)
TUNGESTATES
CaWO4
Schellite
(Ce,La,Nd,Th)(PO4,
SiO4)
Monazite
(8)
PHOSPHATES
Ca5(PO4)3
Apatite
CuAl 6(PO 4)
4(OH) 8·4H 2O
Turquoise
(9)
SILICATES

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(9) SILICATES
➢ A very common mineral group constitutes more than 95% of
the earth’s crust.
➢ Silicate minerals are essentially composed of Si-O4
tetrahedron
➢ Tetrahedra are the basic building blocks of all silicate
minerals.
➢ According to the proportion and arrangement of the Si-O4
tetrahedra, silicate minerals are classified into 6 Categories.

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A. Single Solitary SiO4-Tetrahedron Minerals: Neso Silicates
(Independent or isolated )
➢ These are silicate minerals composed of only ONE Si-O4
tetrahedron ➢ The basic unit is (SiO4)4-
➢ The Si:O ratio is 1:4
➢ They have (-4 free electrons)
example Zircon ZrSiO4
B. Soro Silicates (Twin Tetrahedral Structure)
➢ These are silicate minerals composed of only two Si-O4
tetrahedral. The two silicates are sharing one oxygen.
➢ Basic unit (Si2O7)6-
➢ Has (-6 free electrons)
➢ The Si:O ratio is 2:7,example melilite
Ca2MgSi2O7

32. ➢ Ring of tetrahedral form as two oxygen of each tetrahedron
based on the adjacent tetrahedral in a closed rings.
➢ Ring may link three, four or six tetrahedral
C. Single Ring SiO4-Tetrahedra Minerals: (Cyclo-Silicates)
The basic unit is (SiO3)n , n=3,4,6
1) Triad-Ring Silicate minerals such as:(3-fold)
o The basic unit is (SiO3)3, i.e. n=3
o The Si:0 is 1:3
o Has (-6 free electrons).
Example
Wollastonite…………..CaSiO3
Bentonite ……………. BaTi (SiO3)3

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2) Tetrad-Ring Silicate minerals (4 Fold)
o The basic unit is (SiO3)4, i.e. n=4
o The Si:0 is 1:3
o Has (-8 free electrons).
3) Hexa-Ring Silicate minerals (6 Fold)
o The basic unit is (SiO3)6, i.e. n=6
o The Si:0 is 1:3
o Has (-12 free electrons).
Example
Beryl…………….Be3Al2(SiO3)6

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D. Chain SiO4-Tetrahedra Minerals (Ino silicates)
➢ There are two sub types of these chain silicates (Ino silicates):
1) Single chain silicate
2) Double chain silicate
1) Single Inosilicates (Single Chain Silicates)
➢If two of the oxygen's are shared in a way to make long single chains
of linked SiO4 tetrahedral, we get the single chain silicates or
Inosilicates.
➢In this case the basic structural unit is Si2O6
-4 or SiO3
-2. This group is
the basis for the pyroxene group of minerals, like the orthopyroxenes
(Mg,Fe)SiO3 or the clinopyroxenes Ca (Mg,Fe)Si2O6.

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2) Double Inosilicates (Double Chain Silicates)
➢ If two chains are linked together so that each tetrahedral group
shares 3 of its oxygen's, we can from double chains, with the basic
structural group being Si4O11
-6.
➢ The amphibole group of minerals are double chain silicates, for
example the tremolite-ferroactinolite series Ca2(Mg,Fe)5Si8O22(OH)2.
Amphibole-Mg7Si8O22 (OH)2.

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E. Sheet SiO4-Tetrahedra (Phylo silicate) Minerals
➢ If 3 of the oxygen's from each tetrahedral group are shared such that
an infinite sheet of SiO4 tetrahedral are shared we get the basis for the
Phyllosilicates or sheet silicates.
➢ In this case the basic structural group is Si2O5
-2. The micas, clay
minerals, chlorite, talc, and serpentine minerals are all based on this
structure.

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F. Tecto-Silicates (frame Work silicate)
➢ All the oxygen shared
➢ Si:O=1:2
E.g. Quartz, Feldspars

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2.1.3 Rock-forming Minerals
➢ Although about 3500 minerals are known to exist in the
Earth’s crust, only a small number, between 50-100, are
important because they are common or valuable.
➢ The rock-forming minerals make up the bulk of most rocks in
the Earth’s crust.
➢ They are important to geologists simply because they are the
most common minerals.
➢ They are olivine, pyroxene, amphibole, mica, the clay
minerals, feldspar, quartz, calcite, and dolomite.

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➢ Olivine is an independent tetrahedral silicate mineral that
occurs in small quantities in basalt of both continental and
oceanic crust .
▪ However, rocks composed mostly of olivine and
pyroxene are supposed to make up most of the mantle.
➢ The pyroxenes are a group of single chain silicates
▪ Pyroxenes are a major component of both oceanic
crust and the mantle and are also abundant in some
continental rocks.
A) Silicates Rock forming Minerals

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➢ The amphiboles are a group of double-chain silicates
with similar properties. They occur commonly in many
continental rocks.
➢ The micas are sheet silicates and typically grow as plate-
shaped crystals, with flat surfaces Mica is common in
continental rocks. The clay minerals are similar to mica
in structure, composition, and platy habit.
➢ Feldspar and quartz are group of framework silicates.
The feldspars make up more than 50 percent of the Earth’s
crust. Quartz is abundant in continental rocks but rare in
oceanic crust and the mantle.
A) Silicates Rock forming Minerals

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➢ The silicate minerals contain the (SiO4)4- complex anion.
➢ Silicates make up about 95 percent of the Earth’s crust. They
areso abundant for two reasons.
o Silicon and oxygen are the two most plentiful elements in
the crust.
o Silicon and oxygen combine readily.
Silica
(SiO4)4-
Why silicates are dominant?

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B) Non-silicates Rock Forming Minerals
➢ The complex carbonate anion (CO3)2-is the basis of two
common rock-forming minerals, calcite (CaCO3) and
dolomite [CaMg(CO3)2].
➢ Most limestone is composed of calcite, and dolomite makes
up the similar rock that is also called dolomite or
sometimes dolostone.
Carbonates
Fig. Calcite (a) and dolomite (b) are two rock-forming carbonate minerals.

43. Summary
•Mineral are classified on the bases of their chemical
composition, and the most common once are native minerals,
Oxides, Hydroxides, Halides, Phosphate and Silicates etc.
•Silicates minerals rich rock are most abundant of the Earth’s
crust.
•Olivine, pyroxene, amphibole, mica, feldspar and quartz
are silicate rock forming minerals
•Calcite, and dolomite are non-silicate rock forming minerals
43

44. Thank you
44

45. Today Agenda
•Rock and types of rocks
•Engineering consideration of rocks
46

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2 .2 Rocks
➢ Rock is solid mixture of two or more minerals.
➢ The figure below shows the rock cycle.
Three types of rocks.
▪ Igneous
▪ Sedimentary
▪ Metamorphic
2.2.1 Definition of Rocks And Rock Cycle

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2.2.2.1 Igneous Rocks
➢ Igneous rock is defined as any rock that has cooled from
molten rock.
2.2.2 Types of Rocks

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Intrusive Igneous Rocks - Rocks that cool from a melt
below the ground.
o Example: Granite, Gabbro, pegmatite, Diorite,
Granodiorite etc.
Extrusive Igneous Rocks –Rocks that cool from a melt
above the ground.
o Example Basalt, Scoria, Rhyolite, Ignimbrite, Pumice,
Tuff,, Obsidian, etc.
Classification of Igneous Rocks
A) Based on Mode of Formation

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B) Based on Ferro-Magnesian Content
➢ Igneous rocks are classified into two categories based on
their ferromagnesian content.
(a) Dark (or ferromagnesian) silicates
➢Olivine, pyroxene, amphibole, and biotite mica.
Example, Basalt, Gabbro, Scoria, etc.
Basalt Gabbro

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b) Light (or non-ferromagnesian) silicates
➢ Quartz, muscovite mica, and feldspars
Example, Rhyolite, Ignimbrite Granite, Pumice, Tuff,
Granodiorite etc.
Rhyolite Pumice
Granite

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(i) Granitic (Acidic Rocks)
▪ Termed felsic (feldspar and silica) in composition
▪ High amounts of silica (SiO2)
▪ Light-colored silicates
▪ Major constituent of continental crust
(ii) Basaltic (Basic Rocks)
▪ Termed mafic (magnesium and iron) in composition
▪ Dark silicates and calcium-rich feldspar
▪ Higher density than granitic rocks
▪ Comprise the ocean floor and many volcanic islands
C) Based on Silica Content

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Other compositional groups
(iii) Intermediate (or andesitic) composition
▪ Contain 25% or more dark silicate minerals
▪ Associated with explosive volcanic activity
(iv) Ultramafic composition
▪ Rare composition that is high in magnesium and iron
▪ Composed entirely of ferromagnesian silicates

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1) The use of igneous rocks as aggregate in Portland cement
concrete can cause problems.
▪ Acidic Igneous rocks (igneous rocks with granitic
composition, Pyroclastic rocks, Eg. Tuff, Volcanic
breccia, Obsidian, and Pumice) have high silica content
and thus, they can cause alkali-silica reaction problems
2) Very coarse grained igneous rocks are undesirable for use
as aggregates for construction.
o With increasing grain size, abrasion resistance is
reduced, and the rock is less suitable for use as a base
course (road base), concrete aggregate, or source of
riprap (large stone used for slope protection along rivers
and sea coasts).
Engineering considerations of igneous rocks

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3) The presence of certain minerals in igneous rocks makes the
rock undesirable for some engineering uses.
o Zeolite minerals are undesirable in aggregates that will
be exposed to the weathering process.
4) In foundations for engineering structures such as dams,
bridge piers, and underground installations, weathered
igneous rock and/or any other rock is to be avoided.
o Excavation must extend through this material into sound
rock.
Engineering considerations of igneous rocks

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2.2.2.2 Sedimentary Rocks

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➢ Sedimentary rocks are formed by compaction of clasts, a
chemical precipitate, or and evaporative residue.
o Clast – A particle of a rock.
o Chemical precipitate – a fine powder that comes out of
solution.
o Evaporative residue – a fine powder left over when water
with minerals dissolved in it evaporates.
A) Introduction

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B) Types of sedimentary rocks
➢ Sediment originates from mechanical and/or chemical
weathering.
➢ Hence based on their mode of formation, sedimentary rocks
are classified into two categories.
1) (Clastic) Detrital rocks
o They are sedimentary rocks that are formed from
compaction and cementation of pre-existing rocks
2) (Non-Clastic) Chemical rocks
They are sedimentary rocks formed from compacted
precipitates or evaporate residues.

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1) Detrital (Clastic) sedimentary rocks
➢ Clastic sedimentary rocks are those which were formed
from broken rock pieces.
➢ Thus, these types of sedimentary rocks are differentiated
from one another by particle size.

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Types of detrital sedimentary rocks
Common detrital sedimentary rocks:
(i) Shale
o Mud-sized particles in thin layers that are commonly
referred to as laminea
o Most common sedimentary rock
o Naturally it poses very low bearing capacity
(ii) Sandstone
o Composed of sand-sized particles
o Forms in a variety of environments
o Quartz is the predominant mineral

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o Alternating sequences of shale and sandstone exposed in the Grand
Canyon.
o Shale cannot support steep cliffs or form erosional escarpments

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(iii) Conglomerate and Breccia
✓ Both are composed of particles greater than 2mm in
diameter
✓ Conglomerate consists largely of rounded gravels; often
has a similar appearance to “concrete”
✓ Breccia is composed mainly of large angular particles and
fragments, which have not been rounded
Conglomerate Breccia

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Types of Chemical sedimentary rocks
(a) Limestone
o Most abundant chemical
rock
o Composed chiefly of the
mineral calcite
o It very soluble rock
➢ Consist of precipitated material
that was once in solution.
➢ Precipitation of material occurs
by: (a) inorganic processes, (b)
organic processes (biochemical
origin)
2) Chemical sedimentary rocks
Diagram showing the carbon cycle, with
emphasis on flow of carbon between the
atmosphere and hydrosphere

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(b) Evaporites
➢ Examples include rock salt;
gypsum (used for drywall,
aspirin, and potash (used for
fertilizer)
(c) Coal
▪ Different from other rocks
because it is composed of
organic material
▪ Stages in coal formation (in
order): Plant material, Peat,
Lignite, Bituminous and
Anthracite.

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1) Certain sedimentary rocks can be involved in the alkali-
silica reaction problem in Portland cement concrete.
Eg. Chert.
2) Limestone and dolomite provide the best sedimentary
aggregates for construction materials.
o Siltstone, shale, quartz sandstone, and conglomerate are
generally not acceptable.
3) Coarse-grained limestones abrade too severely to be used
for aggregates for construction.
o Such rock participles lose gradation owing to a reduction
in particle size.
Engineering considerations of sedimentary Rocks

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4) Sedimentary rocks used as dimension stone for the facing of
buildings should be non-staining and resistant to weathering
effects.
5) Limestones, dolomites, and evaporite deposits can exhibit an
irregular soil - rock interface in their weathering profiles.
o Care must be taken to ensure that heavy structures are founded
completely on solid rock.
6) Sinkholes and underground conduits in limestones and dolomites
must be recognized and properly dealt with when founding
buildings in these terrains.
7) When water is impounded behind a dam, if limestone lies at the
rim or within the reservior area, careful consideration is required.
o The presence of solution channels in such rocks can lead to
leakage unless the channels are filled by grouting or other
techniques.

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8) Conglomerates are basically weak sedimentary rocks
because they are poorly cemented and highly porous.
o Water movement through this rock removes the cement
and increases permeability.
o When encountered in dam abutment and foundations,
conglomerates require special treatment to increase
their strength and reduce permeability.
9) Sedimentary rocks containing anhydrite are troublesome to
engineering structures such as dams, highways, and tunnels
because the mineral will alter to gypsum in the presence of
water, yielding an increase in volume and considerable
stress on the structure adjacent to it.
o The presence of anhydrite must be recognized and steps
taken to reduce its effect.

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2.2.2.3 Metamorphic Rocks

68. 69
What are Metamorphic Rocks?
➢ Metamorphic rock: rocks that have been changed by heat
and pressure without melting.
➢ Metamorphism is the transition of one rock into another by
temperatures and/or pressures unlike those in which it
formed.
➢ Metamorphic rocks are produced from:
1) Igneous rocks
2) Sedimentary rocks
3) Other metamorphic rocks
Orth metamorphic rocks that have been originated from
igneous , Example : Gneiss
Para metamorphic rocks that have been originated from
sedimentary rocks, Examples : Marble

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What are Agents of Metamorphism?
➢ Most important agent.
➢ Recrystallization results in new, stable minerals.
➢ Two sources of heat:
1) Contact metamorphism – heat from magma.
2) An increase in temperature with depth due to the
geothermal gradient.
(a) Heat

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(b) Pressure and differential stress
➢ Increases with depth.
➢ Confining pressure applies forces equally in all directions.
➢ Rocks may also be subjected to differential stress which is
unequal in different directions.
Regional metamorphism caused by differential stress associated with
mountain building

71. 72
(c) Chemically active fluids
❑ Mainly water with other volatile components.
▪ Enhances migration of ions.
▪ Aids in recrystallization of existing minerals.
Sources of fluids:
- Pore spaces of sedimentary rocks.
- Fractures in igneous rocks.
- Hydrated minerals such as clays and micas.

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What are types of Metamorphism?
1) Contact or thermal metamorphism
▪ It is the type of metamorphism that is driven by a rise in
temperature within the host rock.
▪ It happens when rock is heated up by an intrusion of hot
magma

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2)Hydrothermal metamorphism
➢ It is a type of metamorphism which occurs when country
rocks are chemical altered by hot, ion-rich water.
Hydrothermal metamorphism

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3)Regional metamorphism
➢ Occurs during mountain building
➢ Produces the greatest volume of metamorphic rock
Regional metamorphism occurs when rocks are squeezed between converging plates
during mountain building.

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➢ Progressive regional metamorphism: from low grade (slate); to
high grade (gneiss)

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Common metamorphic rocks
(i) Foliated rocks
(a) Slate
➢ Very fine-grained
➢ Excellent rock cleavage
➢ Most often generated from low-grade metamorphism of shale,
mudstone, or siltstone
(b) Phyllite
➢ Gradation in the degree of metamorphism between slate and
schist.
➢ Platy minerals not large enough to be identified with the
unaided eye.
➢ Glossy sheen and wavy surfaces.
➢ Exhibits rock cleavage.
➢ Composed mainly of fine crystals of muscovite and/or chlorite.

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Slate (left) and phyllite (right), which is more wavy and shiny)

78. 79

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(c) Schist
o Medium- to coarse-grained
o Platy minerals (mainly micas) predominate
o The term schist describes the texture
o To indicate composition, mineral names are used (such as
mica schist)
Garnet mica schist is a high grade
metamorphic rock where individual
plates of shiny mica are easily visible.
The dark red garnet crystals are called
almandine.

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(d) Gneiss
– Medium- to coarse-grained
o Banded appearance
o High-grade metamorphism
o Often composed of white or light-colored feldspar-rich
layers with bands of dark ferromagnesian minerals

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(a) Marble
oParent rock was limestone or dolostone
oUsed as a decorative and monument stone
oExhibits a variety of colors
Marble is a crystalline rock formed by the metamorphosis of limestone
(ii) Non-foliated rocks

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(b) Quartzite
oFormed from a parent rock of quartz-rich sandstone
oQuartz grains are fused together
Quartzite is a non-foliated metamorphic rock formed from quartz
sandstone. It is very hard and resistant, and can be taxing on
construction equipment.

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1) Foliated metamorphic rocks commonly yields rock pieces
with elongated shapes when crushed.
o These rocks could cause mixing problems in fresh
concrete and directional properties in hardened concrete.
2) Foliated rocks posses prominent directional properties.
o Strength and permeability are affected by the direction of
foliation.
o Care should be taken that loads (from bridges, dams,
buildings, and foundations) are not transferred to
foliated rock masses in a direction closely parallel to the
foliation.
Engineering Considerations of Metamorphic Rocks

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3) Metamorphic rocks may be deeply weathered and the
depth to bedrock is quite variable.
o Care must be taken to found heavy structures, or to located
tunnel alignments, in sound rock whenever possible.
4) Slate, schist, and phyllite are subject to rock over-break
during blasting of rock cuts or tunnels because of their
pronounced rock cleavage.
o High stress concentrations in tunnels may occur for the
same reason.
Engineering Considerations of Metamorphic Rocks

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5) The stability of rock slopes is greatly affected by the
orientation (attitude) of foliation with respect to the rock
slope direction.
o When foliation dips steeply into an opening, rockslides
commonly occur. Rock bolts may be needed to prevent
such failures.
6) Marble is subject to the same problems as limestone.
o Solution cavities and channels may develop, resulting in
similar problems of leakage of reservoir and collapse of
newly formed sinkholes.
Engineering Considerations of Metamorphic Rocks

87. Summary
•Rock is solid mixture of two or more minerals.
•There are three common types of rocks
•Igneous
•Sedimentary
•Metamorphic rocks
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88. Next class
Chapter 3
Geological Work of Natural Agencies
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89. Thank you
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