JNTU B.Tech II MINING GEOLOGY Previous Question Paper (April/May - 2018 - R16)

Olivine belongs to the nesosilicate group, which is characterized by an isolated tetrahedral structure where individual SiO₄ tetrahedra are linked by divalent metal cations (Mg²⁺ or Fe²⁺) rather than by sharing oxygen atoms.

The chemical composition of olivine is represented by the formula:

This represents a solid solution series between the magnesium end-member forsterite (Mg₂SiO₄) and the iron end-member fayalite (Fe₂SiO₄).

Rock-forming minerals are identified and classified based on a set of physical and optical properties that reflect their chemical composition and internal crystalline structure. The primary properties used for recognition include:

• Physical Properties: These include Hardness (resistance to scratching, measured on the Mohs scale), Cleavage (the tendency to break along planes of structural weakness), Fracture (the pattern of breakage when cleavage is absent), Luster (the appearance of the surface in reflected light, such as metallic or vitreous), Color, and Streak (the color of the mineral in powdered form).
• Optical Properties: These are observed using a petrological microscope and include Refractive Index, Pleochroism (change in color when rotated under plane-polarized light), Birefringence, and Extinction angle.
• Crystal Form and Habit: The external shape of the crystal or the characteristic mode of aggregation (e.g., prismatic, tabular, fibrous) provides diagnostic evidence of the mineral's internal atomic arrangement.