Rocks
Rock is mixture of two or more minerals.
Minerals
minerals are naturally occurring inorganic solids homogeneous substance composed of atoms having an orderly and regular arrangement with definite chemical composition and characteristic geometric form.
Example quartz(SiO2), Orthoclase and Olivine.
Classification of Rocks
On the basis of their genesis and structure.
Rock are generally group into three classes
- Igneous
- sedimentary
- metamorphic
Composition of upper 5 kilometre of earth surface.
Igneous Rocks
Solidification of molten magma on beneath the surface of Earth.
Non laminar massive structure and whole make up 95% of earth crust.
Igneous rocks based on mode of origin composition.
- Intrusive or plutonic basic
- Extrusive or volcanic
Intrusive
Solidification at moderate depth of earth surface.
Example granite, and Bassalt
Coarse grained crystals
Extrusive or volcanic
Solidification takes palace surface of Earth.
Example granite.
Fine grain crystals
Igneous rocks based on chemical three types.
- Acid. (65-75%). ----sandstone
- neutral. (55-65%). ---Deorite
- basic. (40-55%). ----- Basalt
Sedimentary rocks
Sedimentary is Latin word 'sedimentum' maining settling.
Sediments derived from the breaking down of Pre existing rocks.
sediments are transported to New palace through wind and water action and deposited in new arrangement and cemented to form sedimentary rocks.
stratification is most common feature of these Rock so these are called a stratified rocks.
They are formed through four stage
- Weathering
- transportation
- deposition
- Diagenesis
Metamorphic rocks
Metamorphic rockspart are those which have undergone some chemical or physical change from its original form.
transformation of igneous and sedimentary rocks under the influence of chemically active liquid and gases and internal heat and pressure.
There are two broad classes of metamorphism
- Thermal
- dynamothermal
Thermal
Change bring about by heat as a dominant factor.
Dynamothermal
Change bring about heat and pressure of combine effect.
Example marble graphite
Weathering
Process of disintegration and decomposition of Rocks and minerals, by physical ,chemical and biological process leading to the formation of regolith.
Regolith
Unconsolidated residue of the weathering or weather rock on the earth surface or above the solid Rocks.
Regolith is upper part.
Weathering process
Different weathering agent.
- Physical /mechanical
- Chemical (decomposition)
- Biological (disintegration and decomposition)
Physical or mechanical weathering process
- Physical condition of rocks
- Change in temperature
- Action of water (Fragmentation, Transportation, Decomposition , and action of freezing)
- Alternate wetting and drying
- Action of glacier
- Action of wind and sand blast
- Atmospheric electric phenomena.
Chemical (decomposition)
- Hydration
- hydrolysis
- solution
- carbonation
- oxidation and reduction
Biological (disintegration and decomposition)
- Man and animal
- Higher plant
- Microorganism
Physical weathering
Broken down of rocks into small pieces by the physical agent is called physical weathering.
Physical condition of rocks
the most important single factor that determine the rate at which the rocks weather.
Change in temperature
alternate expansion and contraction due to diurnal change in temperature is more common in hot and desert region where the surface of rocks weeken
Action of water
Water act as disintegrating, transporting and depositing agent.
Moving water has a great cutting and carrying force.
It forms gallies and ravines.
Action of freezing
Increase in volume due to freezing of subsurface water exerts an enormous outward or side ward pressure which break apart the Rocks.
Alternate wetting and drying
Some minerals expand or increase in volume on wetting and shrink on drying , caused the large number of crack in rocks and ground.
Action of wind and sand blast
Dost storms which transport of material from one place to another.
Chemical weathering
Weathering of rocks into small pieces by the chemical agent.
- Chemical weathering involve transformation of new products.
Feldspars +water = Clay minerals soluble cation and anions.
- Chemical weathering are more effective increase the surface area of rocks.
- Chemical weathering is most important factor for soil formation.
Chemical weathering are
- Hydration
- hydrolysis
- solution
- Carbonation
- oxidation and reduction
Hydration
chemical combination of water or addition of water of crystallization then swelling and increase in volume ,minerals lose their structure , become soft and break.
Hydrolysis
dissociation of H2O into H plus and OH minus ion chemically combined with minerals and bring about change such as decomposition of crystallization structure and formation of new compound.
Solution
Minerals which are soluble in water are removed by the continuous flowing of water.
Rocks develop holes rill or rough surface and decompose.
Carbonation
Combination of carbon dioxide with base. Decomposing the minerals of the rocks and soil.
These are quite effective in weathering of rocks.
Oxidation and reduction
Oxidation is the absorption of oxygen ions on the surface of rocks.
Water takes oxygen from atmosphere and form solution which creates crevice and fissure of rocks.
Biological weathering
Decomposition and disintegration of rocks by the biological agent.
Fungi are active in warm and humid environment.
Bacteria are active in cool and humid environment.
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