vermiculite

Vermiculite is a hydrated phyllosilicate mineral in the mica group, consisting of expandable, sheet-like layers of magnesium, iron, and aluminum silicate that contain water. It occurs as flaky brownish to olive-green crystals and is mined from metamorphic or ultramafic rocks.

When heated rapidly, vermiculite expands dramatically as water is released, producing a lightweight, highly porous material known as expanded or exfoliated vermiculite. This property makes it useful for insulation and fireproofing, as well as a moisture-retentive additive in horticultural media and soils. It can also serve as filler and absorbent in various products.

Vermiculite occurs worldwide and is mined in several countries, including the United States, South Africa, China, and Russia. Some natural deposits have contained asbestos minerals; the Libby, Montana deposit is a well-known example. Modern processing includes testing to reduce contamination, and consumer products from reputable suppliers are recommended.

In horticulture, vermiculite improves aeration and water retention. In construction, expanded vermiculite provides thermal insulation and fire resistance. It is also used in packaging and as a soil amendment to improve moisture-holding capacity and soil structure.