Common Forms/Occurrences: Found in granites and pegmatites Useful Identification Test: Can be split into thin flexible transparent sheets Chemical formula: KAl2(Al,Si3O10)(OH,F)2 Crystal System: Short opaque prisms Colour: Colourless, yellow, brown, or red-brown Streak: White Lustre: Nonmetallic (NM) Cleavage: Excellent in 1 direction Fracture: Sectile; Brittle Hardness: 2 - 2.5 Hardness Search: two Specific Gravity: 2.7 - 3.0