The following comes from the EPA's Information Page on Vermiculite.
Asbestos Contamination In Vermiculite
Asbestos contamination in vermiculite and vermiculite products
has become a national concern to a variety of federal agencies
(EPA, OSHA, CPSC and ATSDR) and to many private citizens
throughout the country. A tremendous amount of has
been made available to the public via print, television/radio
and the Internet. EPA's vermiculite pages provides users with
basic about Vermiculite and its uses, factsheets,
Question and Answer documents, reports and links to EPA
Regional vermiculite pages. Other relevant not
included here, may be available from federal, state and local
governments, industry, trade associations and international
sources. Vermiculite and Its Uses
What is Vermiculite?
Vermiculite is the mineralogical name given to hydrated
laminar magnesium-aluminum-ironsilicate which resembles mica
in appearance. All vermiculite ores contain a range of other
minerals that were formed along with the vermiculite in the
rock. Vermiculite ores from some sources have been found to
contain asbestos minerals but asbestos is not intrinsic to
vermiculite and only a few ore bodies have been found to
contain more than tiny trace amounts.
Vermiculite mines are surface operations where ore is
separated from other minerals, and then screened or
classified into several basic particle sizes. Vermiculite is
found in various parts of the world. Locations of the
predominant commercial mines are in Australia, Brazil, China,
Kenya, South Africa, USA and Zimbabwe.
When subjected to heat, vermiculite has the unusual property
of exfoliating or expanding into worm-like pieces (the name
vermiculite is derived from the Latin 'vermiculare' - to breed
worms). This characteristic of exfoliation, the basis for
commercial use of the mineral, is the result of the
mechanical separation of the layers by the rapid conversion
of contained water to steam. The increase in bulk volume of
commercial grades is 8 to 12 times, but individual flakes may
exfoliate as many as 30 times. There is a color change during
expansion that is dependent upon the composition of the
vermiculite and furnace temperature.
How Is Vermiculite Used?
Vermiculite has been used in various industries for over 80
years. It is used in the construction, agricultural,
horticultural and industrial markets. Generic Applications -
Loose Fill Carriers Lightweight Aggregates Soil Conditioners
Asbestos Substitutions Density Modifiers Absorbents Fire
Protection Industrial Heat Insulation