Class -11 NCERT Fundamental of geography chapter - 5

Minerals and rocks

Introduction 

• The earth is composed of various kinds of element.
• These element are in solid form in the outer layer of the earth and in hot and molten form in the interior.
•  About 98% of the total crust of the Earth is composed of 8 elements like oxygen, Silicon, aluminium, iron, calcium, Sodium, Potassium, and magnesium and the rest is constituted by Titanium hydrogen, Phosphorus, magnesium, sulphur, carbon, Nickel and other elements.
•  The element in the earth's crust are rarely found exclusively but are usually combined with other element to make various substance.
•  These substance are recognised as mineral .

Minerals 

• A mineral is a naturally occurring organic and inorganic substance, having an orderly atomic structure and a chemical composition and physical properties.
•  A minerals composed of two or more elements but sometimes single elements mineral like sulphur, copper, Silver ,Gold graphite at etc.  are found.
•  The basic source of all minerals is the hot Magma in the interior of the earth.
•  When Magma cools, crystals of minerals appear and a systematic series of minerals are formed in sequence to solidify so as to form rocks.
•  Minerals such as Coal, Petroleum and natural gas are organic substance found in solid liquid and gases froms respectively .

Physical characteristics 

• External crystal form - determined by internal arrangement of the molecules -  cubes, Octahedrons, hexagonal, prism etc.
• Cleavage-tendency to break in given direction producing relatively plane surface- result of internal arrangement of the molecules - make cleave in one or more direction and at any angle to each other .
• Fracture - internal molecules arrangement to so Complex there are no planes of molecules : The Crystal will break in an irregular manner, not a long Plains of cleavage .
• Lustre- appearance of a material without raised to colour: each mineral has a distinctive lustre like metallics , silky, glossy at sector 
• Colour -  some minerals have characterized coloured determined by their molecular structure - malachite,  azurite,  chalcopyrite etc. and some mineral are coloured by impurities for example because of impurities quartz may be white green red yellow etc. 
• Streak- colour of the ground powder of any mineral. it may be of the same colour as the mineral or main different malachite  is green and gives green streak fluorite is purple or green but gives a white streak.
•  Transparency - transparent: light rays pass through so that object can be seen plainly light ray pass through but will get diffused so that objects cannot be seen opaque light will not pass at all.
•  Structure - particular arrangement of the individual crystal fine medium for coarse grained :fibrous - separable, divergent: radiating .
• Hardness- relative resistance beingscratched : ten Minerals are selected to measure the degree of hardness from 1 to 10 .

They are :

1. Talc
2. Gypsum 
3. Calcite 
4. Fluorite 
5. Apatite 
6. Feldspar
7. Quartz 
8. Topaz
9. Corundum
10. Diamond 

Some major Minerals and their characteristics

• Silicon and oxygen are common elements in all type of feldspar and Sodium , Potassium ,calcium, aluminium etc.  are found in a specific feldspar variety .
• Half of the earth crust is composed of Feldspar. 
• It has light cream to Salmon pink colour.
• It is used in ceramics  and glass making.

Quartz 

• It is one of the most important component of sand and Granite.
•  It consists of silica.
•  It is a hard mineral which usually insoluble in water .
• It is white or colourless are used in radio and radar.
•  It  is one of the most important component of granite.

 Pyroxene

•  Pyroxene  consists of calcium, aluminium, magnesium, ion and silica .
• Pyroxine forms 10% of earth's crust.
•  It is commonly found in meteorites.
•  It is in green or black colour.

Amphibole 

• Aluminium, calcium , silica, iron magnesium are the major elements of amphiboles .
• They from 7 % of earth's crust .
• It is in green or black colour and is used in  asbestos industry.
•  Hornblende is another form of amphiboles .

Mica

•  It comprises of potassium, aluminium, magnesium, iron, silica etc.
•  It form 4% of earth crust.
•  It is commonly found in igneous and metamorphic rocks .
• It is used in electrical instruments.

 Olivine 

•  Magnesium, iron, silica are major elements of olivine .
• It is used in jewellery.
•  It is usually a greenish crystal often in basaltic rocks.
•  Beside these main mineral like chlorite,  calcite,  magnetic bauxite and barite are also present in some quantities in the rocks.

 Metallic Minerals

 These minerals contain metal content and can be subdivided into three types: 

1. Precious metal : gold ,silver ,Platinum etc. 
2.  Ferrous metal : iron and other metal after mixed with iron to form various kind of steel .
3. Nonferrous metal : include metals like Copper, lead, zinc , tin, aluminium etc. 

Non-Metallic minerals

•  These minerals do not contain metal content Sulphur, phosphates and nitrates are examples of non-metallic mineral.
•  Cement is a mixture of non metallic minerals.

Rocks 

• The earth crust is composed of rocks.
• A rock is at aggregated of one or more minerals.
•  For example, granite is hard so stone is soft.
•  Gabbro is black and quartzite can be milky white.
•  Rock do not have definite composition of mineral constituents.
•  Feldsper and quartz are the most common minerals found found in rocks.
•  There are many different kinds of Rock which are grouped under three families on the basis of their mode of formation.

 They are: 

1. Igneous rock-solid find from Magma and Lava.
2. Sedimentary rocks the result of deposition of fragments of Rocks by exogenous process.
3.  Metamorphic rocks formed out of existing rocks understanding recrystallization.

Igneous Rocks 

• The igneous rocks are form format when Magma cool and solidfiles.
•  The process of cooling and solidification can happen in the earth's crust or on the surface of earth.
•  Igneous rocks are classified based on texture.
• Texture depend upon size and arrangement of grades or other physical condition of materials.
•  Intermediate condition of cooling would result in intermediate size of grain making up igneous rock,  granite, gabbro, pegmatite, basalt, volcanic breccia and tuff are some of the examples of igneous rocks .

Sedimentary Rocks 

• The word 'sedimentary' is derived from the Latin word sedimentum,  which means settling .
• Rocks of the Earth's surface are exposed to denudational agents, and are broken up into various size of fragments .
• Such fragments are transported by different exogenous Agencies and deposited.
•  These deposits through compaction turn into rocks. this process is called lithification. 
• Depending upon the mode of formation, sedimentary rocks are classified into three groups :

1. Mechanically formed - Sandstone, Conglomerate, limeston,shale,  loess etc.  are example: 
2. Organically formed - Geyserite,  chalk,  limestone, coal etc. are some examples .
3. Chemically formed -chert,  limestone , halite, potash etc. some examples

Metamorphic Rocks

•  The word Metamorphic means change of form .
• These rock form under the action of pressure volume and temperature changes.
• Metamorphism is a process by which already consolidated rocks undergo recrystallization and reorganization of materials within original rocks.
•  Mechanical distribution and reorganization of the original mineral with in rocks due to breaking and crushing without any appreciable chemical changes is called dynamic metamorphism .
•  The materials of rocks chemically alter and recrystallized is due to thermal metamorphism .
• There are two types of thermal  metamorphosis contact metamorphism and regional metamorphism.
• Quite often new materials form out of Magma or Lava are added to the rocks.
•  In the process of metamorphism is some rocks grains or minerals get arranged in layers or lines .such an arrangement of mineral or grain in metamorphic rocks is called foliation or lineation.
• Types of metamorphic rocks depend upon original rocks that was subjected to metamorphism.
•  Metamorphic rocks are classified into two major group foliated rocks and non foliated rocks. Gneissoid,  granite, syenite,slate, schist, marble, quartzite etc.  are some examples of metamorphic rocks. 

Rock Cycle 

• Rock do not remain in their original form for long but may undergo transformation .
• Rock cycle is a continuous process through which old Rock are transformed into new ones.
•  Igneous Rocks are primary Rock and other Rock form of these primary Rock.
• Igneous rock can be changed into metamorphic rocks .
• The fragments drived out of igneous and Metamorphic rock from into sedimentaryrock.
•  Sedimentary rocks themselves can be  into fragment and fragments can be source for formation of sedimentary rock.
•  The Crustal Rock and once formed may be carried down into the Mantle throw subduction process and the same meltdown due to increase in temperature in the interior and turn into molten magma, the original source for igneous rocks