Vermiculite is a natural mineral which expands with the application of heat. It is formed by hydration of certain basaltic minerals, and is often found in association with asbestos. The mineral was extracted during the 1960s in Libby, Montana, under the commercial name Zonolite (the Zonolite brand was acquired by the W.R. Grace Company in 1963[1]). Mining operations on the Libby site stopped in 1990 in response to asbestos contamination. The United States government estimates that it is used in more than 35 million homes.

World production of vermiculite in the year 2000 exceeded 500 kilotons (metric). Major producers of vermiculite include China, South Africa, Australia, Zimbabwe, and the United States.

Expanded vermiculite is used as a soil conditioner, as loose-fill insulating and packing material, as an insulating filler for plaster and concrete compounds, and as a carrier for dry handling and slow release of agricultural chemicals. Vermiculite is often used along with perlite as a soil additive for potted plants, and as growing mediums for hydroponics.

Vermiculite is also used in glassblowing, lampwork, and Glass beadmaking work to allow finished, hot pieces to cool slowly.

Cite: Wikipedia