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Rock : 

1. A rock is a natural solid organic or inorganic material forming the crust of the earth. 

2. A rock is an aggregate of minerals. 

3. The physical properties of rocks vary.

Mineral : 

1. The mineral is an organic element or compound which occurs naturally. 

2. A mineral has an atomic structure. 

3. It has fixed definite physical properties.

Rock :  A rock can be defined as “an aggregate of minerals that forms a more or less definite unit of the earth’s crust”. A rock does not possess a definite composition like that of a chemical compounds, but is usually a mixture of various minerals. The bulk of rocks is made up of silica or quartz and feldspar. Feldspar are composed of silica, aluminium, potassium and sodium or calcium. Some rocks are composed of grains cemented together, while several other are crystalline, compact or even glass-like. 

All material (whether hard like stone or sand) of which the crust of the earth is composed are called rocks e.g, stone, clay, lava, sand, chalk, salt, coal marble etc.. On the basis of their mode of formation, rocks are divided into three types : 

1.  Igneous rocks 

2.  Sedimentary rocks 

3.   Metamorphic rocks.

1.  Sedimentary rocks are formed from material derived from other rocks including plant and animal remains. These rocks thus contain fossils.

2.  Sedimentary rocks are generally not crystalline. They are soft and layered as they are formed by deposition of sediments.

1. Sandstone 

2. Limestone

Sedimentary rocks are most widespread on the earth.

Chemically formed sedimentary rocks are formed through chemical action of water. Some mineral like limestones and salts are dissolved into the water and after the evaporation of water form a particular type of rock which is formed by the chemical sedimentation of limestones into gypsum and salt into various types of nitrates.

During the formation of sedimentary rocks, the sediments are deposited in waterbodies and get sorted out according to their size. The sediments accumulate in different layers or strata arranged one above the other. Each layer or stratum has particles of given size. In sedimentary rocks each layer or stratum has particles of a given size. Therefore, sedimentary rocks are also called stratified rocks.

The price of coal increases when it gets metamorphosed into diamonds.

When coal undergoes heavy pressure and intense heat it gets metamorphosed.

The basis for the classification of rocks are their mineral composition, colour and texture.

1. Shale 

2. Mineral 

3. Plutonic rocks 

4. Sill 

5. Conglomerate 

6. Rock salt 

7. Slate 

8. Dynamic metamorphism.

Properties of metamorphic rocks : 

1. These rocks are harder and more resistant than the original rocks. 

2. These rocks have their minerals arranged in a series of bands.

Sedimentary rocks are called Secondary rocks or derived – rocks because they are derived by the denudation of other rocks.

Metamorphic rocks are formed by complete change of texture of rocks through volcanism and diastrophism, e.g., limestone is converted to marble and shale is transformed to slate.

According to the sediments used, the sedimentary rocks are classified into Clastic Rocks, Organically Formed Rocks and Chemically Formed Rocks.

Sedimentary rocks are classified into the following types according to the nature of sediments, their origin, composition and the mode of formation. 

1. Inorganic rocks or Mechanically-formed Sedimentary Rocks :- These type of rocks are formed by the deposition of land derived material. When the river began to flow, they eroded the rocks and washed away to the sea. Clay, shale, sandstone were formed in this way. These rocks are called inorganic rocks. 

2. Organically formed Sedimentary Rocks :- These rocks are formed by the deposition of plants and sea organisms. Millions of years ago, there grew huge forest in marshy places. In course of ages they were buried underground and the internal heat changed them into coal. Moreover, there are millions and millions of sea-organisms whose skeleton are made of Calcium carbonate derived from sea water. After their death skeleton sink to the bottom of the seas and are formed into lime true and chalk and coal. 

3. Chemically-formed Sedimentary Rocks :- There rocks are formed by the evaporation of water from solution containing mineral. Various kinds of salts precipitate from waters of shallow desert lakes, where evaporation of the water is rapid. Gypsum is the best example of this kind of rocks. Several nitrates and potash are also chemically formed sedimentary rocks.

This is a mechanical Transformation in which texture of rocks is changed by crushing and rubbing processes associated with heat and compression created by mechanical action.

There are three types of this type of rocks : 

1. Mechanically formed rocks : Denudation of rocks by agents of change results in layers of sedimentary rocks by mechanism. 

2. Chemically formed rocks : These are formed by evaporation of calcarious water and accumulated along lake and lagoon beds, e.g. gypsum and rock salt. 

3. Organically formed rocks : These are formed by deposition of dead plants and animals e.g. limestone rock (or Calcareous rock) lignite, bituminous and anthracite coal are carbonaceous rocks formed by compression of vegetation under the layers of sedimentary rocks. In the same way petroleum in between the sedimentary rocks is the result of zurasic age dinosaurs e.g. shale rock, containing oil.

The earth is said to be 4700 million years old and the rocks came into existence 3400 years ago. Since then these rocks have undergone various changes by which multiple transformation took place within the rocks. This continuous process of transformation of old rocks into new rocks is known as rock cycle for figure See Page no. of this book.

Lithification means solidification. The loose material carried on by water, wind and ice is deposited slowly in different layers one upon another. Gradually the deposited sediments become solid and hard due to pressure and temperature. Evaporation results in the loss of water within the sediments and these are compacted and cemented. Compaction takes place by increasing weight and pressure of over lying sediments e.g. sand is converted to sandstone. Cementation takes place by bonding of compacted sediments by natural elements like calcium compounds, silica and iron with a property to bind the loose materials to solid state.

Sills : The collection of magma between layers of rocks is called sill. 

Dykes : The fillings of magma in the cracks or fissures of rocks are called dykes

1. Sills: When metamorphism or accumulation of magma found in the internal part of earth occurs horizontally between sedimentary rocks, then this accumulation of solidified magma in the form of layers is called Sills. This accumulation of sills is found in thick form.

2. Dykes: In the internal part of earth, the vertical accumulation of magma in the rocks or in their walls is called Dykes. This accumulation of Dykes is found in long and thin form. This is an internal form of igneous rock like a wall. The organization of Dykes is somewhere hard and somewhere soft.

The magma takes place in between the layers of rocks and hardens after cooling, which is called Sill.

Igneous rocks are associated with volcanic activity, cooling of magma and mechanical weathering etc.

These rocks are formed by consolidation of erupted magma on the surface of earth.

1. Extrusive rocks generally have small crystals because in the formation of these rocks, the solidification of magma takes place at a slower rate. 

2. Silicates are the most common rock forming minerals because they are most common minerals in the Earth’s crust. 

3. Rocks are of great economic significance Some of the main benefits of rocks are as follows : 

(a) After disintergration, they turn into valuable soils. 

(b) They are the store-houses of a large number of minerals. 

(c) They are the source of precious metals like gold, silver, platinum etc. 

(d) They are source of fuel-minerals. 

(f) They provide different types of stones. 

4. The composite zone inhabited by most living creatures is called biosphere. It includes a part of the atmosphere, the hydrosphere and a part of the lithosphere. All three layers are essential for life to exist. As lithosphere is only a small part of the biosphere, therefore, man’s habitat is the biosphere and not the lithosphere in the true sense.

Sedimentary rocks are associated with fossil fuels due to fossils trapped in between layers of these rocks.

Basic igneous rocks have higher percentage of oxides of denser elements and dark in colour, e.g. Basalt, dolerite etc.

Acid Igneous rocks : These are lighter rocks with silica content 65 to 85 percent with density less than 2 g/Cm3, e.g. Granite. 

Basic igneous rocks : These are denser rocks with silica content 40 to 60 percent with average density between 2.8 g/Cm3 and 3.0 g/Cm3 e.g. Basalt.

The rocks contain minerals in the form of ores, but minerals do not contain rocks. Sedimentary rocks contain fossil fuels like coal and petroleum etc, igneous rocks are rich in minerals like copper, gold, iron etc, metamorphic rocks contain valuable building stones like marble and garnet, feldspar etc. Rocks have no definite chemical composition, while minerals have particular chemical composition.

The process of change in the minerals of rock in the form of a solution by the mixing of chemical materials with water is called that Hydro Metamorphism.

When there is hot water on the rocks, then the changes that occur in the rocks due to pressure of water – vapor is called that Thermo – Hydro Metamorphism.

Correct Answer is: (d) Marble

Correct Answer is: (c) Coal

(b) Sedimentary

Correct Answer is: (d) serpentine

The process of change in the form of the igneous and sedimentary rocks and rebuilding of granules in their minerals by the effect of extreme heat is called Thermal Metamorphism.

Correct Answer is: (c) Dolomite

Plutonic rocks : 

1. These are intrusive igneous rocks. 

2. These cool down very slowly due to heat in the interior 

Volcanic rocks : 

1. These are extrusive igneous rocks. 

2. These cool down abruptly due to less temperature on the surface region.

Plutonic rocks are the igneous rocks which are formed as some depth in the earth’s crust, when a molten material gets solidified under pressure. Granite is very good example of a Plutonic rock.

Rocks which are formed by the transportation and deposition of the particles by wind are called Aeolian Rocks.

Rocks which are formed by lime dominated living organisms are called Lime – oriented Rocks.

Rocks which are formed when the magma solidified in the cracks at some depth beneath the earth’s surface are called Hypabyssal Rocks. These are small – sized rocks.

Rocks in which the amount of silica is in between 45% to 55% are called Basic Rocks.

Rocks which are formed when the magma cooled down and solidified at considerable depth beneath the earth’s surface are called Plutonic Rocks.

The rocks found on the earth’s surface are being divided into different parts on the basis of their origin, duration and composition. 

This classification of rocks is being presented in the following table:

Description of Metamorphic Rocks

Definition of Metamorphic Rocks: The different types of rocks made by the basic changes in the properties and structure of the original rocks without their disintegration and dissociation are called Metamorphic Rocks.

Cause of Metamorphism: Metamorphism of the original rocks is due to the effect of mainly water, heat and pressure.

Features of Metamorphic Rocks: Metamorphic rocks are the secondary rocks. These are harder than the original rocks. These rocks are non – porous. Metallic minerals are found in abundance in these rocks.

Classification of metamorphism of the Metamorphic Rocks: Metamorphism of the Metamorphic Rocks are classified into four parts: Thermal Metamorphism, Regional Metamorphism, Hydro Metamorphism and Thermo – Hydro Metamorphism.

Thermal Metamorphism occurs due to extreme high heat. Regional Metamorphism occurs due to compression and heat. Hydro Metamorphism occurs due to action water on chemical materials. Thermo – Hydro Metamorphism occurs due to action of water vapor and pressure.

Classification of Metamorphic Rocks: On the basis of the original rocks, due to whose metamorphism the Metamorphic Rocks are made.

The rocks are being classified into the following parts:

Re – metamorphism of few Metamorphic Rocks like:

Sedimentary rocks were formed after the igneous rocks. Sedimentary rocks are formed by the accumulation of many types of materials and sediments. These rocks are formed by the accumulation of layers over the layers on the fossils of living – organism vegetation and rocks-flour of different rocks. 

These rocks are classified into the following parts:

Classification of Sedimentary Rocks: Sedimentary rocks are formed by many types of materials and sediments. 

These rocks are classified on the following basis:

1. On the basis of the sediments used in formation. 

2. On the basis of the resources used in formation.

1. On the basis of the sediments used in formation: In this classification of rocks, the rocks are classified into clastic rocks, Organically Formed Rocks and Chemically Formed Rocks.

(a) Clastic Rocks: Rocks – flour obtained by the processes of weathering and erosion gets accumulated at a place in the form of layers. Over the passage of time, this accumulation organizes and takes the form of sedimentary rocks. 

Examples: Sandstone, Clay, etc. 

(b) Organically Formed Rocks: Rocks which are formed by the fossils of living – organisms and vegetation are included in this category. This includes lime – oriented and carbon – oriented rocks. 

Examples: Dolomite and Coal – oriented rocks. 

(c) Chemically Formed Rocks: Rocks which are formed when various chemical substances dissolved and solidified are included in this category.

Examples: Alabaster, Gypsum, Sart rock, etc.

2. On the basis of the resources used in formation: On this basis, the sedimentary rocks are classified into three parts: Aqueous Rocks, Aeolian Rocks and Glacial Rocks.

(a) Aqueous Rocks: These rocks are formed by the deposition of sediments in aquatic parts. Like-river rock, sea rock, etc. 

(b) Aeolian Rocks: These rocks are formed by the transportation and deposition of particles by wind; e.g. Loess 

(c) Glacial Rocks: Rocks which are formed by the transportation and deposition of pebbles and boulders by the glaciers.

Rocks which are formed when magma is solidified beneath the earth’s surface are called Intrusive Igneous Rocks.

Different types of rocks formed by the basic changes in the properties and structure of the original rocks without their disintegration and dissociation are called Metamorphic Rocks. These original rocks can be igneous, sedimentary or even metamorphic. This metamorphism is due to the effect of water, heat and pressure.

The igneous and sedimentary rocks are metamorphosed, and few metamorphic rocks are also re – metamorphosed. In this metamorphism, in addition to the complete change in the shape of rocks, the structure of minerals also changes. In this, new shape of old minerals can be formed, new minerals can be formed, rocks can take another shape, granular size of rocks can be changed.

Clastic Rocks: Rock – flour obtained by the processes of weathering and erosion gets accumulated at a place in the form of layers. Over the passage of time, this accumulation organizes and takes the form of sedimentary rocks. Examples: Sandstone, Clay, etc.

Chemically Formed Sedimentary Rocks: Flowing water dissolves the soluble substances in its path, transports them and sets their accumulation elsewhere, due to which these rocks are formed. Alabaster, Gypsum , Tufa are the examples of this type of rocks. In this type of rocks, the soluble substances dissolve with water. Later when the pressure decreases, the water turns into vapor or due to decrease in the speed of flowing water, these dissolved substances start settling down, due to which these rocks are formed.