module 2 - Minerals and Internal Structure of Earth - ERMS.pdf

Earth Resources and
Engineering
JAYARAM NAYAK B
CIVIL DEPARTMENT
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Earthquake:
The engineering geologist studies the seismic nature of the project site.
 He examines the seismic zoning map of the country, evaluates active
and inactive faults and keeps the historical record of the earthquake
of the region in which the civil engineer will prepare a seismic
design of structure.
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Geological features of the civil engineering have to be
studied a detail before execution of the work.
The engineering geologist must work from the exploration
stage to the end of the project.
The civil engineer and the engineering geologist have to
work in the field together either good coordination in order
in order to identify the field problems and to suggest
possible remedial measures in the case of problems of
structures.
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INTERNAL STRUCTURE OF EARTH
Our Earth is a cosmic body. It is one of the nine members
of The Solar system of which Sun is the central star.
The eight planets constituting the Solar system has been
named as Mercury, Venus, Earth, Mars, Jupiter, Saturn,
Uranus and Neptune.
In its shape, the Earth is commonly described as a
spheroid, it has an equatorial diameter of 12,757.776km
and a polar diameter of 12,713.824km and thus has an
equatorial bulge.
At present the Earth is the only planet believed to be
sustaining life other planets have shown no signs of life on
them.
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The Earth's layered structure.
(1) inner core;
(2) outer core;
(3) lower mantle;
(4) upper mantle;
(5) lithosphere;
(6) crust (part of the lithosphere)

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ATMOSPHERE
 The outer gaseous part of earth starting from the surface and extending as far as 700km and
beyond is termed atmosphere.
 Although extending for such great distances, the atmosphere makes only one-millionth
part of the mass of earth; this is because of its gaseous composition.
 It is now fairly established that the atmosphere possesses a layered structure.
 Their well-defined layers or zones of the atmosphere are surface upward, troposphere,
stratosphere and ionosphere.

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LITHOSPHERE
 It is the solid part of the earth and in a broader sense includes all the solid materials
composing the earth from surface downwards, although sometimes-specific terms are used
for deeper earth zones.
 Recent detailed seismic studies of the body of the earth have shown that it is composed of
three well-defined Crust, Mantle, Core.

Depth
Layer
Kilometres Miles
0–60 0–37
Lithosphere (locally varies
between 5 and 200 km)
0–35 0–22
… Crust (locally varies
between 5 and 70 km)
35–60 22–37 … Uppermost part of mantle
35–2,890 22–1,790 Mantle
210-270 130-168
… Upper mesosphere (upper
mantle)
660–2,890 410–1,790
… Lower mesosphere (lower
mantle)
2,890–5,150 1,790–3,160 Outer core
5,150–6,360 3,160–3,954 Inner core
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THE CRUST
Is the topmost shell of the earth, which has a thickness of
30-40 km in the continents and 5-6 km in the oceans.
There is a striking variation in the materials or rocks, as
they are called, composing the crust over the continents
and ocean floors.
The oceanic crust is made up of heavier and darker rocks
called basalts compared to light-colored and light-density,
granitic rocks of the continental crust.
When considered as a part of the total structure of the
earth, crust makes only an insignificant part represented by
a thin layer, similar to the skin of an apple.
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As regards he chemical composition of the crust, analyses made
by Clarke and Gold Schmith, using rocks from different
geographic regions of the crust have all shown that when
expressed in terms of oxides, the crust has Silica as the most
dominant component, its value lying above 50% by volume in
the oceanic crust and above 62% in the continental crust.
Alumina is the next important oxide, varying between 13-16%
followed by Iron Oxides (8%), Lime (6%), Sodium (4%),
Magnesium (4%), Potassium (2.5%) & Titanium (2%).
The crust itself shows a complicated structure both in make-up
and compositional variations.
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 Many rocks now making up Earth's crust formed less than 100 million (1×108) years ago;
however, the oldest known mineral grains are about 4.4 billion (4.4×109) years old,
indicating that Earth has had a solid crust for at least 4.4 billion years.

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THE MANTLE
 At the base of the crust materials of the earth become greatly different in many properties
from those overlying them in the crust.
 These materials appear to form a nearly homogeneous zone till a depth of 2900 km is
reached.
 This zone of materials lying between crust and a depth of 2900 km is known a MANTLE.

It is made up of extremely basic materials, called ultra
basic rocks, which are believed to be very rich in iron and
magnesium but quite poor in silica.
 Such rock names as Periodotites, Dunite.
This One is characterized with a high density, increasing
steadily with depth further; the mantle material is believed
to be highly plastic in nature.
Many of the most important geological process such as
earthquakes and formation of mountains are believed to
have their origin in this zone.
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The mantle is divided into upper and lower mantle.
The upper and lower mantle are separated by the transition
zone.
 The lowest part of the mantle next to the core-mantle
boundary is known as the D″ (pronounced dee-double-
prime) layer.
The pressure at the bottom of the mantle is ≈140 GPa (1.4
Matm).
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THE CORE
 It is the third and the innermost structure shell of the earth, which is clearly marked by the
seismic evidence.
 It starts at a depth of 2900 km below the surface and extends right up to the center of the
earth at 6370 km.
 The material making the core is found to be from seismic studies only strikingly different
from that making the other two shells in one major aspect, in elastic properties.

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 The material has no shear resistance, which makes it nearer to liquid than to a solid body.
 It has a very high density, above 5-6 gms/cubic centimeter, at the mantle –core boundary.
 Nothing can be said about the composition of the core.
 Metallic portion to occupy some 65% of the diameter of the Earth.
 According to one, widely favored view, the inner core is made up of Iron and Nickel alloy
material.

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 The core can be divided on the bases of rock formation:
 The upper layer is called sialic or granitic.
 The lower layer is sima or borattic

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Mineralogy: It’s the branch of geology deals with study of minerals.
Minerals: Minerals its is a substance having a definite, composition, atomic structure formed
from inorganic process in nature.
Minerals have been defined as naturally occurring substances, mostly inorganic, that are
characterized by a definite chemical composition and a definite atomic structure.

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 Since rocks which make up the earth are simply natural aggregates of minerals, a study of
minerals is of fundamental importance understands the elements of science of geology.
 Each mineral is generally characterized with a set of qualities some of which are always
distinctive and differentiate it from other minerals.

Minerals are classified into two groups namely:
1) Rock forming minerals
2) Ore minerals
Rock forming minerals: are those which are essential to
form rock.
Ex: Quartz, Mica etc.
Ore minerals: are those having metal content which are
very essential to start an industry to the development of
country.
Ex: Hematite, Chalcocite etc.
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 Properties may be studied from the body of the minerals, its shape, color, shine, hardness
etc.; these are termed physical properties.
 Some other qualities like the behavior towards light require extremely thin sheets or
sections of the minerals and are best studied with the help of a microscope.
 These are termed optical or microscopic properties.

Physical properties:
1. Colour
2. Streak
3. Lusture
4. Fracture
5. Cleavage
6. Diaphariety
7. Hardness
8. Specific gravity
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Habit
 A mineral may sometimes show a definite and characteristic arrangement in its outer
appearance or physical shape.
 This shape is expressed by the term Habit and is typical in the case of many minerals.

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Some Common Structures in Minerals: 1-Tabular, 2-Columnar ,3-Bladed, 4-Acicular,
5- Fibrous, 6-Reniform, 7-Foliated, 8-Radiating, 9-Granular.

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Fibrous habit: -When the mineral is made up of fibers, generally separable.
Ex. in Asbestos.
Columnar habit: - When the mineral is composed of thin or thick columns, sometimes
flattened.
Ex.in Hornblende.
Bladed habit: - The minerals appears as if composed of thin, blade like structure.
Ex. in Kyanite.

Lamellar habit: - The plates or leaves are separable,
Ex. Vermiculite.
Granular habit: - The mineral shows numerous grains
packed together.
Ex. in Chromite.
Acicular habit: - When a mineral surface is covered
by large, conspicuous, overlapping prominences.
Ex. in Malachite.
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Mammillary habit: - When a mineral surface is covered by large, conspicuous, overlapping
prominences.
Ex. in Malachite.
Reniform habit: - The rounded prominences exhibit a resemblance to a kidney shape.
Ex. in Hematite.
Foliated habit: - When the mineral consists of thin and separable leaves.
Ex.in Mica.

Radiating habit: - When the fibers or needles are
arranged around a central point.
Ex. in Iron Pyrites.
Tabular habit: - The mineral is flat and elongated.
Ex. in Calcite, Orthoclase.
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COLOUR
 Minerals show great variety of colors.
 The color of a substance is its appearance in light and depends upon the composition and
structure of the substance.
 In minerals, colors may be either of inherent of an exotic nature.
 The inherent colour former is related to the chemical composition and is more diagnostic.
 whereas exotic colors are due to small traces of impurities and may vary within wide
limits.
 Metallic minerals commonly show greater consistency in colors than the non-metallic
minerals.

STREAK
 The streak of a mineral is the color of its powder.
 This becomes important in the sense that for some minerals, the
color is entirely different from that of their powder.
 This has been found true in certain or minerals, while most of the
other minerals exhibit a white streak: and, streak does not help in
distinguishing those minerals.
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MINERAL
NAME
ORIGINAL
COLOR
STREAK
COLOR
PYRITE Brass-Yellow Greenish Black
CHROMITE Greenish-Black Greenish Brown
HEMATIE Black Cherry-red

The streak of mineral can be readily observed by
scratching it on a streak plate, which is made up of
unglazed porcelain or roughened glass.
While determining streak for a mineral, care should be
taken to scratch it from its obscure part, and to give only a
small scratch, producing a small quantity of its powder.
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LUSTER
 The shining surface of a mineral is called it luster.
 The different types of luster and their examples are given in a tabular
column.
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S.No.. Type of Luster Description Example
1 VITEREOUS LUSTER A mineral having a glassy shine Quartz and Calcite
2 PEARLY LUSTER A mineral having a pearly shine Muscovite Mica
3 METALLIC LUSTER A mineral having a metallic shine Magnetite
4 SILKY LUSTER A mineral having a silky shine Asbestos
5 RESINOUS LUSTER
A mineral having a greasy, oil
shine Talc
6
ADAMANTINE
LUSTER
A mineral having a diamond like
shine Diamond

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DIAPHENITY
 Diaphaneity of a mineral may be defined as its capability to pass light through it.
 Hence, if an object can be seen fully and easily through a mineral, it may be called as
diaphaneity.
 Depending upon the extent to which light can pass through a mineral, they may be
classified as follows.

Type of
Transparency
Description Example
Transparent
Mineral which allows the light to
pass fully, and objects on Other sides
are seen clearly through the mineral.
Quartz,
Calcite
Translucent
A mineral which allows only
some diffused light to pass through
edges.
Jasper
Opaque
A mineral which does not pass
any light, and hence through which
nothing can be seen.
Orthoclase,
Hornblende
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FRACTURE
 The fracture of a mineral may be
defined as the appearance of its
broken surface, when the mineral
is hammered and broken.
 It is a characteristic feature of
certain minerals, which help us in
their identification.
 The different types of fractures
seen in various minerals.
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Type of Fracture Description Example
EVEN FRACTURE When the broken surfaces of a mineral are smooth Chert
UNEVEN
FRACTURE
When the mineral breaks with very rough and coarse surface Chromite
CONCHOIDAL
FRACTURE
When a mineral breaks with curved surfaces. In fact, there
will be concentric grooves and ridges resembling with the
concentric lines of growth on a shell (Conch)
Quartzite
HACKLY
FRACTURE
When a mineral breaks with irregular surfaces having
sharp edges
Copper
EARTHY
FRACTURE
When a broken surface is soft and almost smooth Chalk
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HARDNESS
Hardness is another property of a mineral, which can be used as a
handy tool in the field, to differentiate between the different minerals or
to recognize particular minerals.
 Hardness of a mineral may be defined as the resistance, which the
mineral offers to scratch.
 This property of a mineral is generally determined by scratching a
given mineral with a mineral of known hardness, so as to obtain the
comparative figure for the hardness of the given mineral.
 Thus for example, if a given mineral gets scratched by a mineral or
metal of hardness say 6, but does not get scratched by that of
hardness 5, then evidently we can conclude that the hardness of a
given mineral lies between 5 and 6. Moreover, the intensity of
scratch procured, will help us to judge whether the hardness
determined is nearer to 5 or to 6
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MINERAL HARDNESS
TALC 1 Can be scratch even by finger nail
GYPSUM 2 Can be scratch even by finger nail
CALCITE 3 Can be scratch even by finger nail
FLUORITE 4 Can be scratch by penknife
APATITE 5 Can be scratch by penknife
ORTHOCLASE 6 Can be scratch by penknife
QUARTZ 7 Can not be scratch by penknife
TOPAZ 8 Can not be scratch by penknife
CORUNDUM 9 Can not be scratch by penknife
DIAMOND 10 It can be scratch by another
diamond
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SPECIFIC GRAVITY
 It is defined as the ratio of its weight to the weight of an equal
volume of water.
 Strictly speaking, the weight of water should be taken at 4o C, as the
temperature variations bring a slight change in the weight of after of
a certain fixed volume.
 In fact, the specific gravity of a mineral depends upon the weight and
spacing of its atoms.
 A mineral possessing heavier and closely spaced atoms will have a
high specific gravity: whereas, a mineral possessing lighter and
widely-spaced atoms will have a low specific gravity.
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 The specific gravity of the mineral is thus, in fact a representation of
its atomic structures.
 All minerals have been found to possess a specific gravity varying
between 1 to 20: but most of them do have specific gravities varying
between 2 to 7.
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Cleavage - The tendency of a mineral to break
along flat planar surfaces as determined by the
structure of its crystal lattice.
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 Cleavage forms parallel to crystallographic planes
 Basal or pinacoidal cleavage occurs when there is only one cleavage
plane. Graphite has basal cleavage. Mica (like muscovite or biotite) also
has basal cleavage; this is why mica can be peeled into thin sheets.
 Cubic cleavage occurs on when there are three cleavage planes
intersecting at 90 degrees. Halite (or salt) has cubic cleavage, and
therefore, when halite crystals are broken, they will form more cubes.
 Octahedral cleavage occurs when there are four cleavage planes in a
crystal. Fluorite exhibits perfect octahedral cleavage. Octahedral cleavage
is common for semiconductors. Diamond also has octahedral cleavage.
 Rhombohedral cleavage occurs when there are three cleavage planes
intersecting at angles that are not 90 degrees. Calcite had rhombohedral
cleavage.
 Prismatic cleavage occurs when there are two cleavage planes in a crystal.
Spodumene exhibits prismatic cleavage.
 Dodecahedral cleavage occurs when there are six cleavage planes in a
crystal. Sphalerite has dodecahedral cleavage.
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I. a. Rock-forming minerals (important-
constituents of rocks). Biotite
b. Minerals of economic value
(important for society) Hematite
II. a. Primary minerals – Product of
consolidation of magma ( magma –
molten silicate lying under the surface
of the earth)
b. Secondary minerals – formed by
operational process on the surface
subsequent to the consolidation of
magma.
- Olivine – primary mineral
Malachite – secondary mineral
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III. a. Essential minerals – presence or
absence affect the naming of the rock.
b. Accessory minerals – no much
importance in the naming of the
rocks.
- Quartz – essential – composition of
granite
Zircon – in granite – accessory
IV. a. Most scientific method – Dana-
the fundamental subdivisions of the
mineral kingdom on the basis of
chemical composition
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i. Native elements
ii. Sulphides
iii. Sulphosalts
iv. Halides
v. Oxides
vi. Oxygen salts
vii.Organic salts
viii.Hydrocarbon compounds
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I. The non-silicate minerals
1. Native elements
2. Halides
3. Sulphides
4. Oxides
5. Carbonates
6. Nitrates
7. Borates
8. Sulphates
9. Chromates
10. Phosphates, arsenates and vanadates
11. Molybdates and tungstates
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II. The silicate minerals
Quartz group
Kaolinite group
Mica group
Feldspar group
Asbestos group
Carbonate group
Gypsum
Ore minerals
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