Rocks and Minerals

The source of all the minerals is hot magma. The 98% of earth’s crust is composed of 8 elements (descending order)- oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium and rest are is constituted by titanium, hydrogen, phosphorous, manganese, sulphur, carbon, nickel and other elements. These elements are found in combined form to make various substances. these
substances are known as mineral(organic(composed of carbon & hydrogen with other element) and inorganic).Minerals such as coal, petroleum and natural gas are organic substances found in solid, liquid and gaseous forms respectively.

    The outer layer of earth’s crust is lithosphere made of granite rocks(form continents) mainly composed of silica and alumina so collectively referred to as sial. The lower part of lithosphere is denser made up of basalt rock forming ocean floor, composed of silica, iron, magnesium collectively called sima. Beneath the crust the next layer is mantle (mesosphere) composed of very dense rock rich of olivine(magnesium iron silicate).the innermost layer is core(barysphere) composed of iron and nickel so known as nife. Part of earth covered by ocean and sea is known as hydrosphere. Fifteen miles skyward the earth is enveloped by mass of gases making atmosphere.

Some important mineral are: -

1.  Feldspar: - main elements are silicon and oxygen but in some specific feldspar sodium, potassium, calcium, aluminium etc are found. half of earth’s crust is made of feldspar. Its color is cream to salmon pink.used in ceramic and glass making

2. Quartz: - it is main component of sand and granite.it consists of silica. it is insoluble in water. Used in radio and radar. It is white or colorless. Most important component of granite.

3. Proxene: - found in meteorites. Made of calcium, aluminium, magnesium, iron and silica. 10% of earth’s crust.

4. Amphibole: - Aluminium, calcium, silica, iron, magnesium are the major elements of amphiboles.7% of earth’s crust.green or black color. used in asbestos industry. Hornblende is another form of amphiboles

5. Mica: - It comprises of potassium, aluminium, magnesium, iron, silica etc. It forms 4 per cent of the earth’s crust. It is commonly found in igneous and metamorphic rocks. It is used in electrical instruments.

6. Olivine: - Magnesium, iron and silica are major elements.It is usually a greenish crystal, often found in basaltic rocks.

7. Besides these main minerals, other minerals like chlorite, calcite, magnetite, haematite, bauxite and barite are also present in some quantities in the rocks.

Mineral are either metallic or nonmetallic.

1. Metallic:  - Which contain metal.

a. Precious metal: gold, silver, platinum.

b. Ferrous metal: other metal mixed with iron to make various kind of steel.

c. Non ferrous metal: copper, lead, zinc, tin, aluminium.

2. Non metallic: - not contain metals. Cement is a mixture of nonmetallic minerals.

Earth’s crust is composed of rock. Rocks are classified into 3 categories according to their origin and appearance. Igneous rocks, sedimentary rocks and metamorphic rocks. Rocks are made up of one or more minerals. Petrology is science of rocks and petrologist study rocks.

1. Igneous rocks:  -

                Solidified form of magma and lava and therefore called primary rocks. Igneous rocks are subdivided based on mineral composition. Rock of high proportion of silica is called acid rocks they are less dense and lighter color eg. Granite and other rocks are basic rocks contain basic oxides such as iron, aluminium or magnesium, these are denser and darker colored. They are crystalline rocks and do not contain fossils.

                Igneous rocks are classified based on texture and texture is based on size and arrangement of grains and other physical condition of material. If molten material is cooled slowly at great depths, mineral grains may be very large. Sudden cooling (at the surface) results in small and smooth grains. Intermediate conditions of cooling would result in intermediate sizes of grains making up igneous rocks. Granite, gabbro, pegmatite, basalt, volcanic breccias and tuff are some of the examples of igneous rocks

 According to origin the igneous rock are of two types.

a. Plutonic rock: - formed in some depth of crust. They are cooled slowly so large crystals are formed. These intrusive rocks (formed inside crust) such as granite, diorite, gabbro are exposed to surface by the process of denudation and erosion.

b. Volcanic rock: - poured out by magma as lava and solidify rapidly so small crystal formed. Basalt is common volcanic and extrusive rock. Some landforms of volcanic rocks are Deccan plateau of India, atrium in north Ireland, Columbia- snake plateau. Some basalt solidity very peculiar manner so they formed polygonal column. Some rocks are very solid so used in making roads and monuments.

2.  Sedimentary rock: - 

                Form from sediments accumulated over a long period of time usually under water. They are different from other rock in characteristic, layer, formation and also called stratified rocks and are fine graind, soft or hard. They bought by streams, glaciers, wind and animals. Lithification is the process in which the sediments are converted into sedimentary rocks. The layers of deposits retain their characteristics even after lithification Hence, we see a number of layers of varying thickness in sedimentary rocks like sandstone, shale etc.

Depending on formation sedimentary rocks are classified into 3 categories.

a) Mechanically formed: these rocks are formed from the accumulation of material derived from other rocks which have been cement together. Sandstones are probably the most familiar sedimentary rocks, formed from sand grains. quartz derived from granite. The finer sedimentary material form clay.  Limestone and shale are also examples.  

b) Organically formed: formed from the remaining of the living organisms such as coral and shellfish. Most common rock formed in this way is Calcareous type e.g. limestone and chalk. The carbonaceous are also organically formed. Plants and animals are compressed by overlaying sediments and they become masses of carbon and converted into coal, peat, lignite. 

c) Chemically formed: formed from precipitation of solution or deposition of solution. Gypsum or calcium sulphate formed from the evaporation of salt lakes, in similar way potash and nitrate is formed. Rock salt obtained from strata (layer of sedimentary rock) which once formed bed of sea.

3.  Metamorphic rock: - 

                All rocks either igneous or sedimentary rocks changed rock under great heat, pressure and temperature. In the process of metamorphism in some rocks grains or minerals get arranged in layers or lines, such an arrangement of minerals or grains is called foliation or lineation. Sometimes minerals or materials of different groups are arranged into alternating thin to thick layers appearing in light and dark shades, Such a structure in metamorphic rocks is called banding and rocks displaying banding are called banded rocks. In this manner clay converted into slate, limestone into marble, sandstone into quartzite, granite into gneiss, shale into schist, coal into graphite etc.