Short notes on the Chemical composition and uses of Garnet

Chemical composition: The general formula of garnet group of minerals is R⁺² ₃R⁺³ ₂[SiOJ₃, where R⁺² is Ca, Mg, Fe⁺² or Mn and R⁺³is Fe⁺³, Cr or Ti.

The group consists of 2 series viz. Pyralspite and Ugrandite. The compositions of minerals belonging to these two series are given in.

(i) Form: Generally granular and crystallized in the form of rhomb- dodecahedron anu trapezohedron of isometric system.

(ii) Colour: The members are differently coloured as given in.

(iii) Luster: Vitreous to resinous.

(iv) Streak: White.

(v) Hardness: 6-8.

(vi) Cleavage: Absent; cracks are often present.

(vii) Fracture: Conchoidal to uneven.

(viii) Specific gravity: 3.5 – 4.3.

(ix) Diaphaneity: Transparent to translucent.

Use:

All varieties are used as abrasive and transparent varieties of almandine; andradite and pyrope are used as gemstones.