Pyrophyllite

Formula: Al₂Si₄O₁₀(OH)₂

Origin of name: from Greek for fire and leaf

Crystal system: triclinic and monoclinic

Crystal class: -1

Twinning: 

Unit cell: a = 5.16 Å, b = 8.97 Å, c = 9.35 Å, a = 91.2°, b = 100.5°, g = 89.6°

Colour: white, grayish white, yellowish, pale blue, greenish, grayish

Diaphaneity: 

Luster: pearly to dull and glistening

Habit: crystals tabular, elongated, subhedral, curved and distorted, foliated, radiated lamellar or fibrous, granular to compact

Hardness: 1 to 2

Specific gravity: 2.65 to 2.90

Cleavage: 1; {001} perfect

Tenacity: laminae flexible, inelastic

Streak: 

Synonyms/varieties:

Comments: data are for pyrophyllite-2M, there is also a -1A polytype