KERALA PSC / PHYSICAL GEOGRAPHY / ROCKS AND MINERALS / NOTES

 

KERALA PSC / PHYSICAL GEOGRAPHY / ROCKS AND MINERALS / NOTES

KERALA PSC / PHYSICAL GEOGRAPHY / ROCKS AND MINERALS / NOTES

 

·       Rocks and minerals mainly constitute the upper part of the earth’s crust. Minerals are natural substances having characteristics properties and more or less specific chemical compositions

·       Rocks are solid materials that make up the earth’s crust. On the basis of texture, structure and composition, rocks may be classified into igneous, sedimentary and metamorphic

·       Igneous rocks are formed by the solidification of molten magma from the interior of the earth. About 95% of the earth’s crust is made up of this type of rocks. It generally do not occur in layers. Most of them are crystalline. Eg: Granite, volcanic rocks and Basalt

·       Also called primary rocks; they are generally hard, massive, crystalline and contain no fossils

·       They are also called Parent Rocks because all the types of rocks have emerged from these rocks

·       Igneous rocks are classified into intrusive and extrusive rocks

·       Intrusive igneous rocks formed due to solidification of lava under the surface of the earth. They have content of silica and poor in metallic minerals. Also called acid lava rocks

·       If the lava has very high melting point it may get solidified at great depths. Rocks thus formed are called plutonic rocks. Granite is a common plutonic rock.

·       Extrusive igneous rocks are formed when the lava reach the surface of the earth and then solidify. It is also called basic lava rocks, eg: Rhyolite, basalt etc…

·       Rocks are formed through solidification of lava in the beds or the layers of earth crust. Some of the molten materials rising from the interior is unable to reach the surface. This material penetrates the joints and fissures in the rocks and solidifier. Here it cools in the form of vertical wall-like structures called dykes

·       Sedimentary rocks are formed from the sediments deposited on the ocean beds. They comprise only about 5% of the earth’s crust, but covers about 75% of the total land surface.

·       Sedimentary rocks are generally softer, fossils are commonly found in these rocks. These rocks are also called stratified rocks.

·       Shale is the most abundant of all sedimentary rocks which is composed of silt and clay.

·       Sandstone is a common sedimentary rock which is formed mainly of quartz particles cemented together by silica, lime or iron oxide

·       Mineral oil or petroleum is derived from organic matter trapped between the layers of sedimentary rocks.

·       Metamorphic rocks are formed when pre-existing sedimentary or igneous rock is altered as a result of changes in physical or chemical conditions. Eg: Quartzite and Marble

·       The process which produces metamorphic rocks is called metamorphism

·       Quartzite is the metamorphic form of the sedimentary rock, sandstone.

·       Slate is formed by the compression of sedimentary rocks like shale and mudstone. Gneiss is formed by the metamorphosis of igneous rocks like granite

·       Chalk is a calcareous rock made up of microscopic skeletal elements from a variety of lime secreting organisms.

·       Coal and Peat represent the accumulation of vegetation which originated in swamps. Peat is the first stage in the transformation of vegetable matter into coal.

·       ‘Black Twins’ is the name given to iron and coal. ‘Black lead’ is graphite. Anthracite is the most superior type of coal.

 

KERALA PSC / PHYSICAL GEOGRAPHY / ROCKS AND MINERALS / NOTES