CBSE Class 11 Geography Minerals And Rocks Notes

 MINERALS AND ROCKS 

This unit deals with

Minerals, elem ents, characteristics of minerals such as crystal form cleavage, fracture,lustre, colour,streak, transparency ,structure, hardness specific grvity, important minerals such as feldspar,quartz,pyroxene,amphibole,mica,olivine and their characteristics classificationof minerals, rocks,igneous,sedimentary ,metamorphic rocks rock cycle

Minerals found in the crust are in solid form where as in intrior they are in liquid form98% of the crust consist of eight elements

1.oxygen                     2. Silicon                    3. Aluminium                     4. Iron.                       5. Calcium 6. Sodium 7. Potassium            8. Magnes

the rest is constituted by titanium, hydrogen, phosphorous, manganese, sulphur carbon, nickel & other elements

Many elements found in combination with other elements. These substances are called minerals Mineral: naturally occuring inorganic substance having an orderly atomic structure and a definite chemical composition and physical properties. 

It is composed of two or three minerals /single element ex. S,Cu, Ag,Au, Graphite. 

There are at least 2000 minerals in the crust. There are at least six mineral groups which form rocks in the crust.

 The basic source of all minerals is the hot magma in the interior of the earth. Coal, petroleum and natural gas are organic minerals 

Tendency to break in given direcations producing relatively plane surfaces, it may any direction

FRACTURE: Conchoidal fracture

Obsidian

Conchoidal fracture is a curved breakage that resembles the concentric ripples of a mussel shell. It often occurs in amorphous or fine-grained minerals such as flint, opal or obsidian, but may also occur in crystalline minerals such as quartz. Sub conchoidal fracture is similar to conchoidal fracture, but not as curved. (Note that obsidian is an igneous rock, not a mineral, but it does illustrate conchoidal fracture well.)

Earthy fracture

Limonite

Earthy fracture is reminiscent of freshly broken soil. It is frequently seen in relatively soft, loosely bound minerals, such as limonite, kaolinite and aluminite.

Hackly fracture

Native copper

Hackly fracture (also known as jagged fracture) is jagged, sharp and uneven. It occurs when metals are torn, and so is often encountered in native metals such as copper and silver.

Splintery fracture

Chrysotile

Splintery fracture comprises sharp elongated points. It is particularly seen in fibrous minerals such as chrysotile, but may also occur in nonfibrous minerals such as kyanite.

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