Nacrite

Formula: Al₂Si₂O₅(OH)₄

Origin of name: from French nacre = mother of pearl

Crystal system: monoclinic

Crystal class: m

Twinning: 

Unit cell: a = 8.97 Å, b = 5.15 Å, c = 15.70 Å, b = 113.7°

Colour: colourless, white, yellowish, brownish

Diaphaneity: 

Luster: satiny, pearly to dull earthy

Habit: crystal tabular, thin, pseudohexagonal, minute, massive, compact, friable or mealy

Hardness: 2 to 2.5

Specific gravity: 2.60

Cleavage: 1; {001} perfect

Tenacity: scales flexible, inelastic

Streak: 

Synonyms/varieties:

Comments: polymorphous with kaolinite, dickite and halloysite