A soil amendment and medium for root cuttings, vermiculite is a hydrous phyllosilicate mineral and 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
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 | (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 | |
English
Etymology
From Latin vermiculus (“wormlet”), for its fibrous nature and tendency to expand into worm-like shapes when heated.
Noun
vermiculite (countable and uncountable, plural vermiculites)
- (mineralogy) A hydrated silicate mineral which expands on heating; it is used in insulation and as a medium for planting.
Translations
Further reading
- David Barthelmy (1997–2025), “Vermiculite”, in Webmineral Mineralogy Database.
- “vermiculite”, in Mindat.org[1], Hudson Institute of Mineralogy, 2000–2025.
