Formula: Mg0.7(Mg,Fe,Al)6(Si,Al)8O20(OH)4.8H2O
Phyllosilicate (sheet silicate)
Specific gravity: 2.3 to 2.7
Hardness: 1½ to 2
Streak: greenish white
Colour: brown, bronze-yellow

Metamorphic environments (typical)
Hydrothermal environments

Vermiculite is an alteration product of iron-bearing phlogopite or biotite. It occurs at the interface between feldspar-rich and iron- and magnesium-rich igneous rocks, and it also occurs in carbonatites and metamorphosed limestone.
Primary vermiculite is unlikely to form at temperatures above 200 to 300oC.
In metamorphic environments it is associated with corundum, apatite, serpentine, chlorite and talc.

Alteration In the zeolite facies clay minerals transform to illite (variety of muscovite), kaolinite and vermiculite.

Common impurities: Ca, Na, K

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