What is Vermiculite?
Vermiculite is a hydrated expandable phyllosilicate material valued in horticulture, insulation and geological collections for its layered structure and heat-driven expansion.
Mineralogy and structure
Reference formula: (Mg,Fe,Al)3(Al,Si)4O10(OH)2·4H2O. Vermiculite is a variable layered material rather than one fixed end-member species. The structure image uses COD 1000036 as a labelled natural representative; heating can remove interlayer water and expand the flakes. Vermiculite is classified with silicates and has monoclinic crystal symmetry. Typical hardness is 1.5–2 on the Mohs scale and specific gravity is approximately 2.3–2.7.
Colour, lustre and habit
Typical colours include brown, bronze, golden-brown, greenish-brown, grey. The usual platy, micaceous, massive habit and pearly, greasy, dull lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Vermiculite forms in or is associated with weathering and hydrothermal alteration of mica-rich rocks, ultramafic rocks and alkaline environments. Important documented localities include South Africa, the United States, Brazil, China, Russia and Australia.
Layered mineral that expands with water and heat
Vermiculite connects everyday materials with crystal chemistry: interlayer water and weakly bonded sheets explain its expansion, softness and usefulness. Colour and source are more informative than a generic brown label.
Collecting and care
Avoid inhaling dust and do not heat unknown material. Store dry, protect thin flakes from crushing and use appropriate industrial safety controls for bulk product.
