asbestos - tremolite (amphibole) asbestos - teaching hand specimen of fibers in a screw-cap pyrex tube

Asbestiform tremolite from the McIlroy Mine, Inyo County, California.

Tremolite is a calcic amphibole which forms a solution series with actinolite and ferro-actinolite. The ideal formula is Ca₂Mg₅Si₈O₂₂(OH)₂ . Tremolite asbestos is fairly uncommon, and most of the tremolite asbestos mined in the US, including from this mine, went to the Powhatan Mining Company in Woodlawn, MD, for the manufacture of the filter used in Gooch crucibles. These specialized  crucibles are used in determining the mass of precipitates, particularly in analytical chemistry.

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.

A customer commented: "Fantastic tremolite asbestos samples. Purchased for an upper division university course on Energy and Mineral Resources. These samples show all the properties I want the students to see."

For more technical information on this tremolite asbestos, in the National Library of Medicine: https://pmc.ncbi.nlm.nih.gov/articles/PMC4784439/pdf/nihms-747130.pdf

You may have to copy and paste the link. It might bring up an AI overview, depending on your browser. There will be a link to the article:  "Read the full study at PubMedCentral." Click there.

The field photo shows the entrance to the short mine adit where a vein of tremolite occurs in the ceiling. The main entrance to the mine appears to have been covered by a rockfall.

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