Vermiculite

Formula: Mg_0.7(Mg,Fe,Al)₆(Si,Al)₈O₂₂(OH)₄.8H₂O

Origin of name: from Latin vermiculare, which means to breed worms

Crystal system: monoclinic

Crystal class: 2/m

Twinning:

Unit cell: 

Colour: colourless, white, yellow, green, brown

Diaphaneity: translucent

Luster: dull to pearly, bronze

Habit: large plates which may have hexagonal shape

Hardness: 1.5

Specific gravity: 2.2 to 2.6

Cleavage: 1; {001} perfect

Tenacity: 

Streak: 

Synonyms/varieties:

Comments: a group of phyllosilicates with the general formula above