Amosite — commonly called brown asbestos — was the second-most widely used type of asbestos commercially, after chrysotile. It was prized for thermal insulation because of its excellent heat resistance and structural strength.

What Amosite Is

Amosite is an amphibole asbestos — the mineral grunerite in its asbestiform variety. The name “amosite” is derived from “Asbestos Mines of South Africa,” which was essentially its only commercial source. Unlike the curly fibers of chrysotile, amphibole fibers like amosite are straight, stiff, and brittle, resembling tiny needles or rods.

Appearance and Where It Was Mined

Amosite ranges from grayish to brown in color. It was mined almost exclusively in the Transvaal region of South Africa and exported worldwide through most of the twentieth century.

Where Amosite Was Used

Amosite’s heat resistance made it a favorite for high-temperature and structural applications:

  • Thermal pipe and boiler insulation (including block and preformed pipe covering)
  • Asbestos-cement sheets and board used in construction
  • Ceiling tiles and acoustic products
  • Spray-applied fireproofing and insulation
  • Insulating cement and lagging on industrial equipment

It was especially common in commercial and industrial buildings, power plants, ships, and refineries where high-temperature insulation was required.

Health Risk

Amosite is an IARC Group 1 human carcinogen. As an amphibole, its straight fibers are more biopersistent — they lodge in lung tissue and resist the body’s clearance mechanisms far longer than chrysotile. For this reason amosite is considered more hazardous than chrysotile and is strongly associated with mesothelioma, lung cancer, and asbestosis. Studies of insulation workers exposed to amosite products have documented some of the highest mesothelioma rates of any occupational group.

Regulatory Status

Amphibole asbestos including amosite has not been mined or imported into the United States for decades, but amosite-containing insulation and building materials installed before the 1980s remain in place in countless older structures and industrial facilities.

If you were diagnosed with mesothelioma, asbestosis, or another asbestos-related disease and were exposed to amosite-containing insulation, ceiling tile, or cement board at a jobsite or in a building, you may be entitled to compensation through asbestos trust funds and civil litigation.