tremolite (amphibole) asbestos - teaching hand specimen of fibers in a screw-cap pyrex tube
Asbestiform tremolite from the McIlroy Mine, Inyo County, California.
The McIlroy Mine exploited an asbestos vein in the Silurian to early Devonian Hidden Valley Dolomite. It was active in the mid -1900s and is now abandoned.
Tremolite is most often found in metamorphosed dolomitic limestones. Its crystals can grow as fine fibrils that are considered asbestiform. Asbestos is a commercial term used to describe the fibrous material. The form of asbestos most commonly used and encountered is the serpentine mineral chrysotile. Amphibole asbestos such as this is much less common.
The asbestos from the McIlroy Mine was mainly sold to the Powhatan Mining Company for use in crucible filters. This mine is the probable source of fibers that served as reference standards used since around 2000 by the Health and Safety Laboratory (UK). Fibers from the McIlroy Mine have been available as standards from NIOSH since 2014.
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