• Very limited, gathered through indirect sources
• Deepest mine- 4 km- Robinson Mine, S.Africa
• Oil well- deepest is 6 km.
• Plenty to be known about the temperatures, thickness, density, pressure and nature of materials inside the earth.
• More or less concentric layers
– Crust- about 33 km thick on an average
– Mantle- upto 2900 km
– Core- outer core from 2900 to 4600 km, Inner Corefrom 5150 km to 6370 km ( radius of the earth)

• Temperature
• Density
• Pressure, and
• Seismic waves

• According to Newton’s laws of gravity, earth’s density as a whole is 5.5 gm/cc
• Sedimentary rocks on the top- 2.7
• Igneous bedrock- 3.0 to 3.5
• Core- 11-12, may rise to 13-14 at the centre
• Reasons
– Pressure of the upper layers
– The core is made up of Fe & Ni having high density

• Gradual increase as depth increases
• Rate of increase- 12°C per km at depth of 100 km
• ROI- 2°C in the next 300 km, 1°C per km below it.
• At this rate, temp at the core of the earth must be around 2900°C- not true
• Mantle- 2200° C
• Outer Core- 3000 ° C
• Inner Core- 5500 ° C

• Pressure also increases with depth
• Two reasons-
– Overlying layers
– Presence of heavier materials at the centre of the earth
• Centre of the earth- pressure about 3500 kilobars
• Gives rise to volcanic eruptions and tectonic forces

• Most important source of information
• P-Waves- longitudional, movement of particles in the direction of propogation of waves, 5 to
6.5 km/sec
• S-Waves- Transverse, movement of particles at right angle to the direction of the waves, 4 km/sec
• L-Waves- travel along the surface of the earth, travel through all mediums, 3 km/sec

• Course and velocities of waves change when they cross boundaries of various layers
• They suffer reflection and refraction travelling through different medium
• Velocity of both P & S waves increases with depth till 2900 km.
• After this, P waves become slower, S Waves disappear
• Near the centre- P waves become fast again
• All waves follow curved paths.

• Outermost layer
• Average thickness- 33 km
• Speed of P Waves- 5 to 6.5 km/sec at the surface
• Speed of P Waves at the Moho- 7 km/sec
• Divided into two parts-
– Si Al- Average density- 2.75 to 2.9 till 100 km max
– Si Ma- Average Density- 2.9 to 4.75 till 2900 km

• Very thick layer
• Velocity of P & S waves increase here
• At Gutenburg Discontinuity- mantle-core boundary- P waves velocity decreases 13 to 8 km/sec ( density increases), S waves disappear.
• Two parts
– Upper Mantle- from surface to 650 km. Upper part called asthenosphere
– Lower Mantle- molten rock

• Radius- 3470 km
– Outer core- 2200 km- liquid Fe & Ni
– Inner Core- 1200 km- solid Fe & Ni.
• S waves cannot pass through the core.
• S wave shadow zone-
• P waves reach the other side of the earth from the focus.
• Density- 11 to 12.

• Rocks- Made up of minerals- TWO OR MORE
• 2000 different minerals identified- 12 common
• These common minerals are formed of 8 most abundant elements- Fe(35%), O
2
(30%), Si(15%),
Mg (13%), Ni ( 2.4%), S (1.9%), Ca (1.1%) and
Al(1.1%)
• Most abundant minerals constituting the earth’s crust- O
2
(46%), Si(28%), Al (8%), Fe(6%), Mg(4%)
, Ca(2.4%), Potassium(2.3%) & Na(2.1%)

• Chemical substances- elements or compounds
• Metallic and non-metallic
• Iron, copper, lead, gold- metallic
• Gypsum, quartz, mica- non-metallic
• These organize in different ways to form rocks.
• Important mineral groups- in combinations:
– Silicates
– Carbonates
– Sulphides
– Metals

• Important group- 87% of the minerals of the earth’s crust.
• Minerals included- quartz and feldspar
• Quartz- Si & O
2
, hard and resistant
• Feldspar- most abundant silicate, very weak, decomposes very quickly through chemical weathering, used in glass and ceramics industry.

• Much susceptible to chemical weathering
• Most important mineral- Calcite
• Reacts vigorously with carbonic acid, forming karst topography
• Calcite very useful in agriculture, iron and steel industry, chemical industry and in optics.

• Sulphur compounds of metals, rock forming minerals of many deposits of non-ferrous metals.
• Formed mainly by endogenous processes ( internal)
• Pyrites, iron sulphides main minerals
• Form ferric hydroxides and sulphuric acids when they come in contact with water or air.

• Iron
• Aluminium
• Form metal oxides when they come in contact with atmospheric oxygen.
• Commercially important

• Aggregate of minerals- inorganic
• May have only one mineral constituent- rock salt or limestone
• More than two minerals also.
• Three categories- based upon their formation
• Igneous
• Sedimentary
• Metamorphic

• Derived from ‘ignis’ meaning fire
• Cooling and solidification of molten materialsmagma or lava
• Also called ‘parent rocks’ or ‘primary rocks’.
• Classified on the basis of their
– Chemical composition
– Texture
– Location

• Mafic igneous rocks- mostly Si and Mg, dark in colour, basic in nature
• Felsic igneous rocks- mainly contain feldspar,
Si and Al in combination with Na, Ca and
Potassium, light in colour, acidic in nature

• Texture- sizes and patterns of the mineral crystals present., depends on the rate of cooling of magma or lava
• Rapid cooling- small crystals and vice-versa
• Extreme sudden cooling- non-crystalline glass finish
• Slow cooling- great depths, gases trapped
• Fast cooling- lava on earth’s surface, gases escape

• Extrusive- also called volcanic rocks
– Mineral crystals very small- hardly recognized
– Fine grained rocks
– Rains almost absent in Obsidian
– Basalt- typical example
– Covers about 5,00,000 sq. km area in India.
– Known as Deccan Traps
– Building roads, regur soil on weathering

• Intrusive- Plutonic
• Solidification of magma at great depths (pluton)
• Rate of cooling- very slow
• Mineral crystals- very large
• Granite- grey, pink, red or white
• In India- Chattisgarh, Jharkhand, Rajasthan and in parts of the Himalayas
• Building stones.

• Hypabassal Igneous rocks
• Magma gets solidified in cracks and joints.
• Cools quicker than plutonic rock, medium sized crystals.
• Various shapes taken by these rocks-
Batholiths, sills, dykes.
• Dolerite and Pegmatite

• Hard, massive and compact
• Crystal size depends on rate of cooling of magma or lava
• Not layered
• Free of fossils
• Non- porous, water cant easily enter
• Not easily weathered
• Rich in minerals

• Great source of metal ores
• Iron, nickel, copper, lead, zinc, tin, mica, manganese, gold, etc.
• Granites and basalts are used extensively as building materials
• Basalt weathers to regur or black soil
• Basalt also used as a road metal.

• Only 5% of the volume of the earth’s crust
• Widespread in extent
• Formed by deposition of materials deposited by agents of denudation, stratified rocks
• Formed due to process called lithification
• Rocks buried deeper get more dense and hard
• Types-
• Clastic
• Non-Clastic

• Sediments consisting of particles removed individually from parent rock- clastic rocks
• Sediments made up of two basic typeschemical precipitates and organically derived sediments.
– Rock Salt & Gypsum
– Coal and limestone

• Organic sedimentary rocks- formed by organic matter derived from plant and animal remains
– Limestone- shells and skeletons of dead marine animals. Chalk and talc are other examples
– Coal- decay and decomposition of plant remains
– Rock salt, gypsum & saltpetre- rocks formed due to precipitation of minerals from their solutions.
• Inorganic- weathering, erosion and deposition of regolith. Sandstone, shale

• Layered, stratified
• Have ripple marks left by water
• Contain fossils
• Most of the rocks are porous
• Pervious- water can enter
• Do not have crystals
• Much softer than other type of rocks, more prone to weathering and erosion

• Source of iron ores, phosphates,
• Building stones, material for making cement.
• Petroleum is found mostly in areas of these rocks
• Sources of some of rich soils
• Historical monuments in India made from red sandstone.

• Original characteristics of rocks are changedpartly or wholly by heat and/or pressure
• Different types of metamorphism depending upon the agent and zone of influence
– Dynamic Metamorphism- caused by pressure
– Thermal Metamorphism- caused by high temp.
– Zone of influence
• Regional metamorphism- large areas affectedintrusion or deep burial and earth movements
• Contact metamorphism- at igneous intrusions- limited area- 2 km.

• Great hardness
• Closely banded structures
• Interlocked crystals
• During process of change
– New and precious minerals are born
– Crystals are enlarged and rearranged
– Addition of new minerals changes rock composition

• Very useful materials- gneiss, quartzite, anthracite, graphite, marble, slate etc.
• Gneiss, marble-building stones
• Slate-roofing and paving, slate for children
• Graphite- making pensils

• Igneous Rocks-
– Most of the Deccan Plateau- Basalt
– Half of this has been reduced due to erosion
– Area covered- 5 lakh sq.km
– Also found in parts of Saurashtra and Kutch,
Maharashtra, Malwa Plateau and northern
Karnataka, parts of Andhra Pradesh & Tamil Nadu,
Jharkhand & UP
– Dolerite and gabbro also found in these regions

• Sedimentary Rocks-
– Whole of the northern plains
– Materials brought from himalayas and the central highlands
– Approximate depth of rocks- 5500 metres
– Coastal plains, especially the eastern coastal plains
– The delta regions of Mahanadi, Godavari, Krishna
& Kavery rivers

• Metamorphic Rocks
– Schist, gneiss, slate, marble, quartzite- widely spread in Rajasthan, Jharkhand, Madhya Pradesh,
Chattisgarh, Tamil Nadu
– Himalayan region, faulting and folding leads to metamorphism of the sediments of the erstwhile
Tethys Sea