Vermiculite
| Vermiculite | |
|---|---|
 |
|
| General | |
| Category | Phyllosilicates |
|
Formula (repeating unit) |
(Mg,Fe+2,Fe+3)3[(Al,Si)4O10](OH)2·4H2O |
| Strunz classification | 9.EC.50 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/m |
| 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, shiny, light brown |
| 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 | |
Vermiculite is a hydrous phyllosilicate mineral. It undergoes significant expansion when heated. Exfoliation occurs when the mineral is heated sufficiently, and the effect is routinely produced in commercial furnaces. Vermiculite is formed by weathering or hydrothermal alteration of biotite or phlogopite. Large commercial vermiculite mines currently exist in Russia, South Africa, China, and Brazil.
Vermiculite was first described in 1824 for an occurrence in Millbury, Massachusetts, US. Its name is from Latin vermiculare, to breed worms, for the manner in which it exfoliates when heated.
It typically occurs as an alteration product at the contact between felsic and mafic or ultramafic rocks such as pyroxenites and dunites. It also occurs in carbonatites and metamorphosed magnesium rich limestone. Associated mineral phases include: corundum, apatite, serpentine and talc. It occurs interlayered with chlorite, biotite and phlogopite.
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