Short notes on the Physical properties and uses of Biotitic


Chemical composition: K (Mg, Fe) 3(AlSi3O10) (OH) 2. There is considerable substitution of Fe+2, Fe”3 and A1 for Mg, A1 for Si and Na, Ca, Ba, Rb and Cs for K. F may replace some OH.

Physical properties:

(i) Form: Foliated books of pseudo-hexagonal crystals and also disseminated as irregular grains or flakes or foliated masses.


(ii) Colour: Black, greenish black and brownish black.

(iii) Lustre: Vitreous to splendent; pearly on cleavage planes.

(iv) Streak: White.

(v) Hardness: 2-3.


(vi) Cleavage: Perfect 1 set basal.

(vii) Fracture: Uneven.

(viii) Specific gravity: 2.7 – 3.2.

(ix) Diaphaneity: Transparent to translucent, (ix) Tenacity: Flexible and elastic.


Use: Biotite is used as insulator in electrical industry, manufacture of lubricants, wall-finishes, artificial stone, rubber tyres, pharmaceutical industry and to give gloss to wallpaper.

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