Formula: Mg0.7(Mg,Fe,Al)6(Si,Al)8O20(OH)4.8H2O
Phyllosilicate (sheet silicate), smectite group
Crystal System: Monoclinic
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)
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 (DHZ 3 p255).
In metamorphic environments it is associated with corundum, apatite, serpentine, chlorite and talc (DHZ 3 p255).


At lots 10 and 11 of concession 1, Bathurst Township, Lanark County, Ontario, Canada (DeWitts corner), the deposit is located in the Grenville Geological Province, which consists mostly of marble, gneiss, and quartzite. Syenite-migmatite was also reported in the area where the vein-dikes are located. Characteristic features of the vein-dikes include the fact that perfectly formed euhedral crystals of different minerals can often be found floating in calcite with no points of contact with the walls. Sometimes these crystals have inclusions of calcite, irregular or rounded in shape. It has been argued that at least some of the vein-dikes were formed as a result of melting of Grenville marble.
Vermiculite forms yellow 1-mm flakes replacing phlogopite (R&M 97.6.556-564).


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

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