Lepidolite

Formula:  K(Li,Al)₃(Si,Al)₄O₁₀(F,OH)₂

Origin of name:  From Greek for scale

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning:  Rare on {001} about [310] axis

Unit cell: a = 5.21 Ǻ, b = 9.05 Ǻ, c = 20.19 Ǻ, β = 99.1°

Colour:  Pink to purple, colourless, white, grayish, yellowish

Diaphaneity: 

Luster:  Pearly

Habit:  Crystals tabular, pseudohexagonal or hexagonal; thick cleavable masses, coarse to fine scaly; aggregates of books

Hardness:  2.5 to 3

Specific gravity:  2.8 to 3.3

Cleavage:  3; {001} perfect, micaceous, {110} and {010} imperfect

Tenacity:  Flexible, inelastic

Streak:  Colourless

Synonyms/varieties:

Comments:  Data are for Lepidolite-2M; there are also -2M/1 and -2M/2 polytypes