Chemical composition: KA12 (AlSi3OI0) (OH)r Minor substitution of Na, Rb and Cs for K, of Fe+2, Fe+3, Li, Mn, Ti, Cr for A1 and of F for OH are common.
(i) Form: Foliated books of pseudo-hexagonal crystals, massive or disseminated scales and as irregular grains or flakes or foliated masses.
(ii) Colour: Colourless and transparent in thin sheets. Thicker blocks are translucent with light shades of yellow, brown, green and red.
(iii) Lustre: Vitreous; pearly on cleavage planes.
(iv) Streak: White.
(v) Hardness: 2-3.
(vi) Cleavage: Perfect 1 set basal.
(vii) Fracture: Uneven, ragged.
(viii) Specific gravity: 2.76 – 3.
(ix) Diaphaneity: Transparent to translucent, (ix) Tenacity: Flexible and elastic
Use: Muscovite is used to cover lanterns, lamp chimneys and oil stoves.
It is used as insulator in electrical industry, manufacture of lubricants, wall-finishes, artificial stone, rubber tyres, pharmaceutical industry and to give gloss to wallpaper. Powdered muscovite is used to give the frost effect on Christmas cards and Christmas trees. It is also used in manufacture of mica (glimmer) plate, used in petrological microscopes.