2. Geological Processes
• The planet Earth is in a constant state of change
• They modify the Earth’s surface by causing erosion and destruction
of existing rocks
• deposition and formation of new sediments in the seabeds
• creation of new rocks underground and thereby subsequently
affecting further deformation to them with time, adding to the
complexity of ground conditions.
• The driving force for all these geological processes is the energy
from the hot interior of the Earth.
3. Geology
• Geology is the science that deals with the origin,
age, composition, internal structure, surface
features and history of the Earth. It includes the
processes taking place inside the Earth,
discovering its mineral wealth, and techniques to
preserve the Earth. It also deals with the
evolution and modifications of various surface
features like mountains, rivers, coastlines, etc.
• Geology may also be defined as an applied
science to advance our understanding of the
processes that can result in natural disasters such
as earthquakes, tsunamis, landslides, floods, etc.
Therefore, it may be said that geology is the
study of the Earth.
6. Terrestrial &
outer planets
• Inner planets are made
up of rocks and metals
and are quite dense
• while the outer planets
have a smaller density
and are made up of ice
and gases.
• For example, the
density of Saturn is even
less than water.
8. THE ATMOSPHERE
• Atmosphere is the outer gaseous envelope extending up to 700
km beyond the Earth’s surface and is energized by the sun.
• The survival of the life processes is associated with it.
• The atmosphere makes only about one-millionth part of the
total mass of the Earth. Of the total mass of the atmosphere,
99 per cent is within the height of about 32 km from the
surface of the Earth and is held around the planet due to
gravitational pull of the Earth.
• The atmosphere has a layered structure. The different layers of
the atmosphere are distinguished from each other on the basis
of change in composition (chemical), temperature (thermal),
and degree of ionization and so on.
10. Chemical Composition of the Crust
• Silica (SiO2) It is the most dominant
component in the Earth crust and
is more than 50% by volume in the
oceanic crust and above 62% in the
continental crust.
• Alumina (Al2O3) It varies between
13 to 16%.
• Other Components These are iron
oxide (Fe2O3): 8%; lime (CaO): 6%;
sodium oxide: 4%; magnesium
oxide: 4%; potassium oxide: 2.5%;
and titanium oxide: 2%.
• The solid aggregate that makes the crust of the
Earth is called rock.
• The crust is made up of different types of rocks—
the igneous, the sedimentary, and the
metamorphic.
• The crust of the continental regions is divided into
two layers:
• The sial—the upper layer rich in silica and
alumina, of sp. gr. 2.65 and granitic in character;
and
• sima—the lower layer rich in silica and
magnesia, of sp. gr. 3.0 and basaltic in character.
It may be noted that under oceans, only sima
layer is found.
11. Most
Abundant
Elements
of Earth's
Crust
Approximate % by weight Oxide
Approximate %
oxide by weight
O 46.6
Si 27.7 SiO2 60.6
Al 8.1 Al2O3 15.9
Fe 5.0 Fe as FeO 6.7
Ca 3.7 CaO 6.4
Na 2.7 Na2O 3.1
K 2.6 K2O 1.8
Mg 1.5 MgO 4.7
Ti 0.44 TiO2 0.7
P 0.10 P2O5 0.1
12. Age of
Earth
Charles Darwin estimated the age of the Earth about 57 million years on the
basis of the separation of the moon from the Earth.
Kelvin estimated it to be around 20–40 million years on the basis of cooling
of the Earth.
Another crude approach was based on the rate of sedimentation and
thickness of the Earth. But this approach was rejected in a short interval of
time since the rate of sedimentation is different in different parts of the
globe.
The studies of Helmholtz revealed that the Earth is as old as 22 million years
on the basis of emission of heat from the sun.
However, all these methods resulted in varying and unreliable estimates of
the age of the Earth.
13. Radiometric Dating
• All rocks and minerals contain long-lived radioactive elements that were incorporated
into the Earth when the solar system was formed.
• Spontaneous breakdown or decay of atomic nuclei is termed as radioactive decay that
forms the basis of radiometric dating methods.
• Spontaneous breakdown or decay of atomic nuclei is termed as radioactive decay that
forms the basis of radiometric dating methods.
• The technique consists in the measurement of the radioactive material that the rock
contains or the amount of natural atomic fission that has occurred in the rock. The
method is based on the fact that a radioactive
• isotope of an element changes into an isotope of another element at a fixed rate. Each
radioactive element has its own rate, expressed in terms of its half-life.
14. • The most commonly used
radioisotope for the purpose
of determining the age of the
Earth is Uranium-238.
• It changes into a series of
other radioisotopes before a
stable (non-radioactive)
isotope is formed. Since the
rate at which Uranium-238
becomes lead-206 is known,
the age of the rock that
contains Uranium-238 can be
determined from the ratio of
Uranium-238 to lead-206.
The age of the Earth predicted by this method is
at least 2.0 billion years.
Thereafter, addition of the geochemical concept
with radioactive minerals, give an estimate of the
age of the Earth to about 4.6 billion years.
15. RadioCarbon Dating
• Radiocarbon dating uses the decay of C-14 (unstable
isotope) to C-12 (stable isotope) for determining the age
of organic materials.
• When an organism dies, it contains a ratio of C-14 to C-
12, but as the C-14 decays with no possibility of
replenishment, the ratio decreases at a regular rate (the
half life of C-14).
• The measurement of C-14 decay provides an indication
of the age of any carbon based material.
16.
17. A chemist determines that a sample of petrified wood has a carbon-
14 decay rate of 6.00 counts per minute per gram. What is the age of
the piece of wood in years? The decay rate of carbon-14 in fresh
wood today is 13.6 counts per minute per gram, and the half life of
carbon-14 is 5730 years.
1) Determine decimal fraction of C-14 remaining:
6.00 / 13.6 = 0.4411765
2) Determine how many half-lives have elapsed:
(1/2)n = 0.4411765
n log 0.5 = log 0.4411765
n = 1.18057
3) Determine length of time elapsed:
5730 yr x 1.18057 = 6765 yr
18. The carbon-14 decay rate of a sample obtained from a young tree is
0.296 disintegration per second per gram of the sample. Another
wood sample prepared from an object recovered at an
archaeological excavation gives a decay rate of 0.109 disintegration
per second per gram of the sample. What is the age of the object?
Solution:
1) Determine decimal fraction of C-14 remaining:
0.109 / 0.296 = 0.368243
2) Determine how many half-lives have elapsed:
(1/2)n = 0.368243
n log 0.5 = log 0.368243
n = 1.441269
3) Determine length of time elapsed:
5730 yr x 1.441269 = 8258 yr
19. The C-14 content of an ancient piece of wood
was found to have three tenths of that in
living trees (indicating 70% of the C-14 had
decayed). How old is that piece of wood?
Solution:
1) Determine decimal fraction of C-14 remaining:
0.300 (from text of problem)
2) Determine how many half-lives have elapsed:
(1/2)n = 0.300
n log 0.5 = log 0.300
n = 1.737
3) Determine length of time elapsed:
5730 yr x 1.737 = 9953 yr
20. Minerals
• A mineral is a substance or chemical compound that is normally crystalline and that has been
formed as a result of geological processes.
• Mineral may also be defined as a naturally and inorganically occurring substance that is solid (with
exceptions of metallic mercury and water), stable at room temperature, has definite physical
properties and specific chemical composition (but not necessarily fixed), can be represented by a
chemical formula and has an ordered atomic structure.
• Minerals possess a set of constant physical properties. Therefore, they can be described by various
physical properties which relate to their chemical composition.
• Difference in chemical composition and crystal structure distinguish their various species. However,
determination of crystal structure and chemical composition requires extensive laboratory tests and
therefore for field identification of minerals, the physical properties are utilized.
• It may also be taken note that the physical and chemical properties of the minerals are influenced
by the mineral’s geological environment of formation.
21.
22. • As of today, there are about 4,900 known
mineral species, and with the progress of
research one or two elements are added
every year. Over 2,000 minerals have been
found in the Earth’s crust and only less than
10 accounts for over 90 per cent of the
Earth’s crust.
• All the minerals in turn are made of atoms
of chemical elements. Despite so many
naturally occurring elements, the most
common Earth’s crust forming elements in
decreasing order of their abundance are
oxygen, silicon, aluminium, iron, calcium,
sodium, potassium and magnesium. Of
these silicon and oxygen are the most
abundant elements which combine to form
the mineral silicate group known as
silicates.
24. Habit
• Habit is the term mineralogists use
when referring to the crystal
structure and shape of a mineral.
Some minerals have distinctive
shapes. For example, some are
shaped like cubes. Others may be
shaped like prisms or pyramids.
25. Colour
• This is how a mineral
appears when we look at it.
More than one mineral can
have the same colour. This
makes colour not the best
property to use when
classifying minerals. People
also use a streak test to look
at the colour of minerals.
26. Streak
• It is the colour of powdered mineral and is a more
reliable and consistent indicator than the body
colour of the mineral.
• The mineral is scraped, knifed or rubbed across a
streak plate, made up of unglazed hard porcelain,
and is seen by observing any mark left.
• Harder minerals than streak plate do not yield any
colour of the powder.
• It is a diagnostic property for certain ore minerals,
e.g. haematite, the streak of which is cherry red,
but its colour is steel grey or iron-black.
27. Lustre (or Luster)
• This refers to the way light
reacts with a mineral.
Minerologists use
adjectives like metallic,
nonmetallic, dull, greasy,
pearly and waxy to
describe lustre.
• For example pyrite has a
metallic
lustre. Gypsum has a
pearly lustre and talc has a
dull lustre.
Non-metallic: Vitreous, Pearly, Admantine, Greasy, Resinous, Earthy
28. Hardness
• The hardness of minerals
is measured using
the Mohs scale of
mineral hardness. To test
the hardness of a mineral,
the mineral is scratched
using different objects.
The tougher the object,
the harder the mineral.
29. Translucency
• This refers to how see-
through a mineral is. Some
minerals are transparent. This
includes minerals like quartz.
Some minerals
are translucent. These
minerals let some light pass
through, but not detailed
shapes. Others are opaque.
This means you cannot see
through them at all.
30. Cleavage
• This refers to how a mineral
breaks. If a mineral breaks
along a flat surface or a
geometric shape, then the
mineral has cleavage. The
mineral on the right has
cleavage in many different
directions.
The tendency of a mineral to break along a certain definite
direction and yield almost a smooth plane surface is called
cleavage.
31. Specific Gravity
• It is a physical property of mineral
and is defi ned as a ratio of weight of
mineral in air to its weight in water.
• Since it is a relative value, it is
determined experimentally. The
specific gravity of common silicate
minerals is about 2.65. This implies
that they are 2.65 times as heavy as
water.
32. Uses of minerals
Minerals are used to make products that
we use every day. This includes things like
houses, pots and pans, electronics,
batteries, automobiles and even fertiliser.
Valuable minerals include base metals,
industrial minerals and precious metals.
33. • Base metals are metals such as
copper, lead, iron, nickel, tin, zinc and
aluminum.
• Precious metals are metals of high
value, such as gold, iron and platinum.
• Industrial minerals are minerals that
do not contain any metals.
34. FORMATION OF MINERALS
The processes that are responsible for the genesis of minerals
are:
• solidification—hot molten magma solidifies through cooling;
• sublimation—wherein the gaseous form of minerals are formed through
evaporation and precipitation;
• recrystalization—in which minerals are formed due to recrystalization
during metamorphism
• evaporation—wherein the materials dissolved in water solution
crystallize on precipitation under suitable geo-environmental
conditions.
35. Solidification of Magma
• The magma is a natural hot melt with great variation in its chemical
composition, original temperature, viscosity and related physical and
chemical properties.
• The magma continues in the molten state, until surrounding
physiochemical environment changes. The factors such as temperature,
pressure and viscosity and their changes are responsible for the
crystallization of minerals and formation of mineral grains in solid form.
• The presence of some catalytic substances like water vapours, carbon
dioxide, sulphur dioxide, chlorine, fluorine and boric acid greatly facilitates
the process of formation of minerals from the magma and enhance the
process of crystallization. These catalytic substances are called
mineralizers.
• The composition and physical properties of minerals are governed by the
rate of cooling and surrounding geological environment.
• the most common minerals are silica and feldspar rich in general, and
quartz in particular.
• a few quite rare and precious minerals are diamond, ruby, sapphire and
aquamarine
36. Sublimation
• This process is generally associated with
volcanism and fumaroles. In the process of
sublimation, the mineral is formed through
evaporation and precipitation directly from
gaseous state, because of the sudden
cooling of the vapours emanating from
volcanoes or fumaroles.
• Sublimation may occur either near dormant or
active volcanoes. The examples of minerals
formed by this process through dormant
volcanoes are gypsum and halite (table salt).
Native sulphur and pumice like minerals are
derived from the active volcanoes
37. Recrystallization
• Recrystallization is a phenomena in which
the mineral grains which have been already
crystallized are placed for recrystallization
due to changes in pressure and temperature
(i.e. metamorphism).
• Consequently, there is a change in the
atomic structures of the minerals with or
without a change in their chemical
composition.
• minerals of chlorite group (alumino silicates
of Mg, Fe, Ni and Cr, etc.)
38. Evaporation
• In the process of evaporation, the
materials dissolved in water solution
precipitate under suitable geo-
environmental conditions.
• Some of the examples of minerals formed
in the process of evaporation are gypsum
and anhydrite.
39. CRYSTAL
GEOMETRY
• The crystal form of a mineral is the
outward expression of the molecular
structure
• which is dependent on the state of
equilibrium due to the interatomic forces.
• Crystal geometry which is also known as
crystal morphology deals with faces and
forms of crystal.
40. Plane of Symmetry
• It divides crystal into two halves such that one
half of the crystal is the mirror image of other. A
crystal may have more than one plane of
symmetry or even devoid of it.
41. Centre of Symmetry
• It is central point about which every face and edge of crystal is matched by one parallel to it on the
opposite side of the crystal.
42. Axis of Symmetry
• It is a line or an axis through a
crystal about which the crystal
can be rotated to bring it into an
identical position a number of
times in the course of one
revolution.
• Such axis is termed diad (two
fold), trid (three fold), tetrad
(four fold) and hexa (six fold).
• For example, if during the
course of full rotation of 360°
about an axis of symmetry, the
crystal is brought into an
identical positionsix times, the
axis is hexa.
43. When these unit cells are combined with possible “centering” there are
14 different Bravais lattices.
In general, six parameters are required to define the shape and size of a unit cell,
these being three cell edge lengths (conventionally, defined as a, b, and c),
and three angles (conventionally, defined as , , and ). In the strict mathematical
sense, a, b, and c are vectors since they specify both length and direction.
is the angle between b and c, is the angle between a and c, is the angle
between a and b. The unit cell should be right handed. Check the cell above with
your right hand
UNIT CELL TYPES and THE SEVEN CRYSTAL SYSTEMS
Cubic a = b = c. = = = 90º.
Tetragonal a = b c. = = = 90º.
Orthorhombic a b c. = = = 90 º.
Monoclinic a b c. = = 90º, 90º.
Triclinic a b c.. 90º.
Rhombohedral a = b = c. = = 90 º.
(or Trigonal)
Hexagonal a = b c. = = 90º, = 120º.
Orthorhombic
a
c b
