Importance of Minerals in Rocks

We are in the vicinity of minerals all around us. Minerals form the basis for the formation of rocks and their deposits form basins and fertile deltas.

The number of minerals present in the earth crust is in numerous. However, only 30 minerals are found to be present in abundance.

Classification of minerals is done on the basis of their colour, texture, form, lustre, birefringence cleavage, specific gravity and hardness.

Colour: The colour of the crystal is the characteristic feature of different minerals. Every mineral absorbs light of a particular bandwidth and reflects the rest. This reflected light appears to be the colour of the mineral. For example, quartz has vitreous to glassy colour.

Fracture: Every mineral bears a tendency to break under stress. The cracks developed can be irregular and called a fracture. However, sometimes the split takes place along well-defined planes giving a regular surface and is called cleavage. For example, quartz breaks along a cleavage called conchoidal.

Lustre: Every mineral possesses the property of reflecting light which imparts shining on its surface this is called lustre. For example, the brilliance of the diamond is adamantine( brilliant).

Hardness: Hardness is the resistance to abrasion offered by a mineral and is measured using a Mohs scale. The scale has a grading of one to ten in order of increasing hardness with Talc at number one, and Diamond at number 10. The hardness of all the other minerals can be calculated about them( if a mineral leaves a streak line over the other this means that the former is less hard). Similar tests of abrasion can be carried out using a copper coin, iron key, aluminium plate, etc.)

Specific gravity: It is the density of an object on water minerals have an SG varying from 2.65 to 6.7 specific gravity is calculated using the Archimedes principle where loss of weight of an object immersed in water calculated, and the density of the mineral is worked out.

Birefringence: This property depends on the optical activity shown by the crystal when it a source emanating white light passes through it. For an isotropic mineral, its birefringence is zero whereas the value given for a particular mineral is the average taken from the different refractive Index shown by the same mineral.

Form: Minerals can exist in various of ways. The word form refers to the geometry in which they crystallise this depends on the geological conditions on which a mineral faces exposure.( minerals found deep inside the earth crust due to high magmatic activity exist in the form of large crystals called porphyroblasts, However when the magma extrudes over the ground due to the rapid rate of cooling it gets crystallised into crystals of extremely fine size as seen in volcanic igneous rocks.

Identification of minerals is crucial both for a civil engineer and a geologist for the construction of dams, bridges rails and tunnels. Therefore thorough information about them is essential.

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