Geology - Combined Technical Services

1. Introduction to Geology

Geology is the scientific study of the Earth, including its origin, structure, composition, history, and the processes that continuously shape it. It helps us understand rocks, minerals, fossils, earthquakes, volcanoes, groundwater, natural resources, and environmental changes. Geology plays an important role in engineering, mining, petroleum exploration, groundwater management, disaster mitigation, and environmental conservation.

Branches of Geology

Physical Geology – Earth's materials and geological processes.
Historical Geology – Earth's history through geological time.
Mineralogy – Study of minerals.
Petrology – Study of rocks.
Structural Geology – Rock deformation and tectonic structures.
Stratigraphy – Rock layers and their sequence.
Paleontology – Fossils and ancient life.
Economic Geology – Mineral and energy resources.
Hydrogeology – Groundwater.
Engineering Geology – Geological applications in construction.
Environmental Geology – Human impact on Earth.

2. Origin and Interior of the Earth

The Earth formed about 4.54 billion years ago from the solar nebula. Initially molten, it differentiated into layers based on density.

Internal Structure

Crust

Continental crust: Granite, average thickness 35 km.
Oceanic crust: Basalt, thickness 5–10 km.

Mantle

Extends to 2900 km.
Mainly peridotite.
Upper mantle contains asthenosphere where convection currents occur.

Core

Outer core: Liquid iron and nickel.
Inner core: Solid iron and nickel.
Responsible for Earth's magnetic field.

Important Discontinuities

Conrad Discontinuity
Mohorovicic (Moho)
Gutenberg
Lehmann

3. Plate Tectonics

The lithosphere is divided into tectonic plates moving over the asthenosphere.

Types of Plate Boundaries

Divergent

Plates move apart.
Mid-ocean ridges.
New crust formation.

Convergent

Plates collide.
Mountain building.
Subduction.
Volcanoes.

Transform

Plates slide past.
Earthquakes.
Example: San Andreas Fault.

Evidence

Continental drift.
Seafloor spreading.
Paleomagnetism.
Earthquake distribution.

4. Earthquakes

An earthquake is the sudden release of energy due to movement along faults.

Terms

Focus (Hypocenter)
Epicenter
Seismic waves

Types of Seismic Waves

P Waves

Fastest.
Travel through solids, liquids and gases.

S Waves

Travel only through solids.

Surface Waves

Most destructive.

Measurement

Richter Scale – Magnitude.
Modified Mercalli Scale – Intensity.

Causes

Plate movement.
Volcanic activity.
Mining.
Reservoir-induced earthquakes.

Earthquake Zones of India

India has Zones II to V.

Highest risk:

Himalayas
Northeast India
Kutch
Andaman & Nicobar Islands.

5. Volcanoes

A volcano is an opening through which magma reaches the surface.

Types

Active
Dormant
Extinct

Lava Types

Basaltic
Andesitic
Rhyolitic

Landforms

Shield volcano
Composite volcano
Cinder cone
Lava plateau
Caldera

India has only one active volcano: Barren Island (Andaman Sea).

6. Minerals

A mineral is a naturally occurring inorganic solid having definite chemical composition and crystalline structure.

Physical Properties

Colour
Streak
Lustre
Hardness
Cleavage
Fracture
Specific gravity
Crystal form

Mohs Hardness Scale

Talc
Gypsum
Calcite
Fluorite
Apatite
Orthoclase
Quartz
Topaz
Corundum
Diamond

Rock Forming Minerals

Quartz
Feldspar
Mica
Amphibole
Pyroxene
Olivine
Calcite

7. Crystallography

Crystallography studies crystal forms and symmetry.

Crystal Systems

Cubic
Tetragonal
Orthorhombic
Monoclinic
Triclinic
Hexagonal
Trigonal

Crystal Elements

Axis
Plane
Centre of symmetry

8. Petrology (Study of Rocks)

A rock is an aggregate of minerals.

Igneous Rocks

Formed by cooling of magma.

Intrusive

Granite
Gabbro
Diorite

Extrusive

Basalt
Rhyolite
Andesite

Characteristics

Crystalline
Massive
No fossils

Sedimentary Rocks

Formed by deposition.

Examples

Sandstone
Limestone
Shale
Conglomerate

Characteristics

Layered
Fossil-bearing

Metamorphic Rocks

Produced due to heat and pressure.

Examples

Marble
Quartzite
Slate
Gneiss
Schist

Rock Cycle

Magma → Igneous → Sedimentary → Metamorphic → Magma

9. Weathering

Weathering is the breakdown of rocks in situ.

Physical Weathering

Frost action
Temperature variation
Exfoliation

Chemical Weathering

Oxidation
Hydration
Hydrolysis
Carbonation

Biological Weathering

Plant roots
Burrowing animals
Human activity

10. Geomorphology

Study of landforms.

Agents

Rivers
Wind
Glaciers
Sea waves
Groundwater

River Landforms

Erosional

V-shaped valley
Gorge
Waterfall

Depositional

Flood plain
Delta
Alluvial fan

Wind Landforms

Sand dunes
Loess
Mushroom rock

Glacial Landforms

Cirque
U-shaped valley
Moraine

Coastal Landforms

Sea cliff
Beach
Spit
Lagoon

11. Structural Geology

Study of rock deformation.

Primary Structures

Bedding
Lamination

Secondary Structures

Fold
Fault
Joint
Cleavage

Fold Types

Anticline
Syncline
Monocline
Overturned fold

Fault Types

Normal
Reverse
Thrust
Strike-slip

Importance

Oil exploration
Mining
Engineering structures

12. Stratigraphy

Study of rock succession.

Principles

Superposition
Original horizontality
Cross-cutting relationship
Faunal succession

Geological Time Scale

Precambrian
Paleozoic
Mesozoic
Cenozoic

Indian Stratigraphy

Dharwar System
Cuddapah Basin
Vindhyan Basin
Gondwana System
Deccan Traps

13. Paleontology

Study of fossils.

Fossil Types

Body fossils
Trace fossils
Moulds
Casts

Importance

Age determination
Evolution
Petroleum exploration
Paleoenvironment

Index Fossils

Characteristics

Wide distribution.
Short geological range.
Easily recognizable.

14. Economic Geology

Study of economically valuable minerals.

Metallic Minerals

Ferrous

Iron
Manganese

Non-ferrous

Copper
Lead
Zinc
Aluminium

Precious

Gold
Silver
Platinum

Non-metallic Minerals

Limestone
Gypsum
Mica
Graphite
Clay

Fuel Minerals

Coal
Petroleum
Natural Gas
Uranium

15. Mineral Deposits

Formation

Magmatic
Hydrothermal
Sedimentary
Residual
Placer
Metamorphic

Ore

A rock containing valuable minerals in economically recoverable concentration.

Gangue

Worthless associated material.

Grade

Percentage of useful mineral.

16. Coal and Petroleum Geology

Coal

Stages

Peat
Lignite
Bituminous
Anthracite

Major Coalfields

Jharia
Raniganj
Bokaro
Singrauli
Neyveli (Lignite)

Petroleum

Forms from marine organic matter.

Major Indian Basins

Mumbai Offshore
Assam
Krishna-Godavari
Cambay
Cauvery

17. Hydrogeology

Groundwater occurs below Earth's surface.

Aquifers

Confined
Unconfined
Perched

Properties

Porosity
Permeability
Transmissivity
Storage coefficient

Groundwater Problems

Over-extraction
Salinity
Fluoride
Arsenic
Pollution

Conservation

Rainwater harvesting
Artificial recharge
Watershed management

18. Engineering Geology

Application of geology in civil engineering.

Site Investigation

Rock type
Faults
Groundwater
Slope stability

Dams

Important geological considerations:

Foundation strength
Seepage
Reservoir leakage
Earthquake safety

Tunnels

Problems

Fault zones
Water seepage
Rock bursts

Landslides

Causes

Heavy rainfall
Earthquakes
Deforestation
Excavation

Control

Drainage
Retaining walls
Afforestation
Rock bolting

19. Remote Sensing and GIS

Remote Sensing

Collection of information without physical contact.

Applications

Mineral exploration
Groundwater mapping
Land use
Disaster management

GIS

Computer-based system for spatial data.

Components

Hardware
Software
Data
People
Methods

Applications

Urban planning
Resource mapping
Environmental monitoring

20. Environmental Geology

Deals with interaction between humans and Earth.

Environmental Issues

Mining pollution
Soil erosion
Desertification
Climate change
Waste disposal

Sustainable Mining

Mine reclamation
Afforestation
Water management
Waste reduction

21. Marine Geology

Study of ocean floor.

Features

Continental shelf
Continental slope
Abyssal plain
Mid-ocean ridge
Ocean trench

Resources

Offshore oil
Gas hydrates
Manganese nodules

22. Indian Mineral Resources

India is rich in:

Iron ore
Bauxite
Manganese
Limestone
Mica
Chromite
Coal

Major producers:

Odisha
Jharkhand
Chhattisgarh
Karnataka
Rajasthan
Andhra Pradesh
Tamil Nadu

23. Geology of Tamil Nadu

Tamil Nadu mainly consists of Archaean crystalline rocks.

Important Rock Formations

Charnockite
Granite Gneiss
Khondalite
Quartzite

Important Mineral Resources

Lignite – Neyveli
Limestone – Ariyalur
Magnesite – Salem
Graphite – Sivaganga
Granite – Madurai, Krishnagiri
Garnet sands – Tirunelveli
Ilmenite & Monazite – Coastal districts

Important Groundwater Regions

Cauvery Delta
Hard rock aquifers
Coastal aquifers

24. Geological Survey of India (GSI)

Established in 1851.

Functions

Geological mapping
Mineral exploration
Landslide studies
Earthquake investigations
Geo-hazard assessment
National geological database

25. Important Geological Terms

Magma – Molten rock below surface.
Lava – Molten rock on surface.
Dyke – Vertical igneous intrusion.
Sill – Horizontal intrusion.
Batholith – Large intrusive body.
Laccolith – Dome-shaped intrusion.
Xenolith – Foreign rock fragment.
Ore – Economically valuable mineral deposit.
Weathering – Breakdown of rocks.
Erosion – Removal of weathered material.
Denudation – Combined weathering and erosion.
Lithosphere – Rigid outer Earth.
Asthenosphere – Plastic mantle layer.
Isostasy – Gravitational balance of crust.
Fault – Fracture with displacement.
Fold – Bending of rock layers.

TNPSC CTS Geology – Important One-Liners

Earth age: 4.54 billion years.
Thickest Earth layer: Mantle.
Hardest mineral: Diamond.
Most abundant mineral group: Feldspar.
Most abundant igneous rock: Basalt.
Major continental rock: Granite.
India's active volcano: Barren Island.
Fastest seismic wave: P-wave.
S-wave cannot travel through liquids.
Moho separates crust and mantle.
Gutenberg discontinuity separates mantle and outer core.
Lehmann discontinuity separates outer and inner core.
Rock cycle continuously transforms rocks.
Coal rank increases from Peat → Lignite → Bituminous → Anthracite.
Fossils occur mainly in sedimentary rocks.
Granite is an intrusive igneous rock.
Marble is metamorphosed limestone.
Quartzite forms from sandstone.
Slate forms from shale.
Charnockite is a characteristic rock of Tamil Nadu.
Neyveli is famous for lignite.
Geological Survey of India was established in 1851.