Asbestos

Chrysotile

Labeled Old Dominion Mine, Pinal County, but likely from Gila County, Arizona.

This is the mineral chrysotile, a hydrous magnesium silicate named from Greek words meaning “gold fiber” for its silky, chatoyant (“shimmering”), and sometimes golden fibrous appearance. It’s more commonly some shade of green.

You can see in the photo with the millimeter scale how fine these tiny hairs can be, often smaller than one one-hundredth of a millimeter thick. But they are brittle, and when they break, the tiny pieces can become airborne. If they are inhaled over time, they do very unpleasant things to lungs.

For these health reasons, use of asbestos has plummeted from a high (in the US) of 803,000 tons in 1973 to only 150 tons in 2023. 70% of the 2019-2022 consumption by the US was imported from Brazil, which is the fourth largest producer of asbestos in the world. Russia produces almost 50% of the world total and contributed the other 30% of US imports; Kazakhstan mines 20%, and China and Brazil mine 15% each. Worldwide total production was still around 1,300,000 metric tons in 2023. Although that was down significantly from two million tons in 2000, global demand is expected to continue, especially for construction materials in Asia (USGS Mineral Commodity Summaries 2024).

There are a handful of other minerals that can have this asbestiform fibrous habit and may be called asbestos (and are regulated as such), including anthophyllite, tremolite, and actinolite (photo above), but with a few exceptions most of the asbestos mined historically and today is the mineral chrysotile, Mg₃(Si₂O₅)(OH)₄. Asbestos and asbestiform refer to the physical shape of the material, not its chemistry.

Why is any asbestos still used at all? In the US, all of it, only 150 tons, tiny in the list of mineral commodities generally, is consumed in the chloralkali industry, which uses permeable diaphragms of asbestos to form a barrier between chlorine and sodium hydroxide, which would otherwise react violently. The chloralkali process breaks up common salt, sodium chloride, to make chlorine and sodium hydroxide, which are chemicals critical for all sorts of products, from polyvinyl chloride (PVC) to the lye used to make soaps. Chlorine derived mostly from salt is used in making paper, paint, medicines, textiles, and for water purification, and sodium hydroxide is used in the manufacture of aluminum metal, ceramics, glass, and more. Newer membrane cell technology can obviate the need for asbestos and is increasing as a means of providing barriers between reactive chemicals in production.

For its other common uses, including brake pads in vehicles, gaskets, tiles, some wallpapers, and other applications, there are plenty of substitutes for asbestos, and there’s no known production of those commodities in the United States using asbestos, but some finished products are still imported that contain it. That’s not much of a problem until and unless those products fray or are otherwise demolished, releasing asbestos particles.

In March 2024 the US Environmental Protection Agency issued a final rule banning all imports of chrysotile asbestos for any purpose, with a further ban on most aftermarket asbestos products such as brake pads, to be effective in March 2026. The European Union banned asbestos in 2005, but, as everywhere, it is still present in older construction; in 2023 the E.U. reduced tenfold (to 0.01 fibers per cm³) the maximum exposure limits for workers on such buildings.

The deadly asbestos problems at Libby, Montana, were mostly associated with mining and milling which released particles from vermiculite, and with insulation products in which the asbestos was loosely contained. (Most of the asbestiform minerals at Libby are actually unusual amphiboles like winchite and richterite rather than chrysotile; Brandli and Gunter, 2006, Inhalation Toxicology, 18:949–962.)

Vermiculite is a discrete micaceous mineral, Mg_0.7(Mg,Fe,Al)₆(Si,Al)₈O₂₀(OH)₄ · 8H₂O, that forms usually by alteration of other micas like biotite. It exfoliates and expands on heating, which makes it a great product for loose insulation, potting soil, and similar materials. The problem at Libby wasn’t the vermiculite itself, but the asbestiform impurities in it. The Rainy Creek deposit near Libby, Montana, is in an unusual ultramafic igneous body (magnetite and biotite pyroxenite) associated with syenites, intruded into Belt Supergroup rocks about 94 million years ago (Montana, 2006, The Rainy Creek alkaline ultramafic igneous complex near Libby, Montana: Northwest Geology, The Journal of the Tobacco Root Geological Society, v. 35, p. 11-16; Boettcher, 1967, The Rainy Creek alkaline-ultramafic igneous complex near Libby, Montana: J. Geology, v. 75, p. 526-553. Art Boettcher and Art Montana are the same person; he changed his name.).

Don’t worry about the fact that I have this chrysotile specimen sitting in a cabinet on display in my house. I have no plans to grind it up and snort it.

The word asbestos comes from Greek meaning ‘unquenchable,’ applied by the physician Dioscorides (c. 40-90 a.d.) to quicklime (calcium oxide), but this came to have the sense of ‘incombustible’ and was applied to the fibrous minerals about 1600.