Vermiculite | |
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General | |
Category | Phyllosilicates |
Formula (repeating unit) | (Mg,Fe2+,Fe3+)3[(Al,Si)4O10](OH)2·4H2O |
IMA symbol | Vrm[1] |
Strunz classification | 9.EC.50 |
Crystal system | Monoclinic |
Crystal class | Prismatic (2/m) (same H-M symbol) |
Space group | C2/m |
Unit cell | a = 5.24 Å, b = 9.17 Å c = 28.6 Å; β = 94.6°; Z = 2 |
Identification | |
Color | Colorless, white, yellow, green, brown, black |
Crystal habit | As large crystalline plates to clay-sized particles; lamellar to scaley |
Cleavage | Perfect on {001} |
Tenacity | Pliable |
Mohs scale hardness | 1.5–2 |
Luster | Greasy or vitreous (pearly at cleavage planes) |
Streak | White or yellowish, translucent, shiny, light-brown or greenish in color, in some cases. For example, palabora vermuculite. |
Diaphaneity | Translucent |
Specific gravity | 2.4–2.7 (0.065–0.130 when exfoliated) |
Optical properties | Biaxial (−) |
Refractive index | nα = 1.525 – 1.561 nβ = 1.545 – 1.581 nγ = 1.545 – 1.581 |
Birefringence | δ = 0.020 |
Pleochroism | X in paler shades than Y and Z |
References | [2][3][4] |
Vermiculite is a hydrous phyllosilicate mineral which undergoes significant expansion when heated. Exfoliation (other links: A, B) occurs when the mineral is heated sufficiently; commercial furnaces can routinely produce this effect. Vermiculite forms by the weathering or hydrothermal alteration of biotite or phlogopite.[3] Large commercial vermiculite mines exist in the United States, Russia, South Africa, China, and Brazil.
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