Phyllosilicate (sheet silicate)
Specific gravity: 2.3 to 2.7
Hardness: 1½ to 2
Streak: greenish white
Colour: brown, bronze-yellow
Common impurities: Ca, Na, K
Metamorphic environments (typical)
Vermiculite is an alteration product of iron-bearing phlogopite or
It occurs at the
interface between feldspar-rich and iron- and magnesium-rich igneous rocks,
and it also occurs in carbonatites and
Primary vermiculite is unlikely to form at temperatures above 200 to 300oC (DHZ 3 p255).
In metamorphic environments it is associated with corundum, apatite, serpentine, chlorite and talc (DHZ 3 p255).
In the zeolite facies clay minerals transform to muscovite variety illite, kaolinite and vermiculite.
Back to Minerals