Vermiculite
Vermiculite is a hydrous phyllosilicate mineral which undergoes significant expansion when heated. Exfoliation 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. Large commercial vermiculite mines exist in the United States, Russia, South Africa, China, and Brazil.
| Vermiculite | |
|---|---|
| General | |
| Category | Phyllosilicates |
| Formula (repeating unit) | (Mg,Fe2+,Fe3+)3[(Al,Si)4O10](OH)2·4H2O |
| IMA symbol | Vrm |
| 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 | |
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