Amphibole refers to a group of dark-colored silicate minerals that is typically composed of iron and magnesium ions. Grunerite, better known as amosite, belongs to this mineral group. Amosite was the second most commercially used form of asbestos after chrysotile. It comprised approximately five percent of all the asbestos used in building materials.
What Does Amosite Asbestos Look Like?
Grunerite became commercially known as amosite because one of the most important suppliers of this form of asbestos was the Asbestos Mines of South Africa or AMOSA as these mines were commonly called.
It is often referred to as “brown Asbestos” because of its color. Amosite fibers are thicker and much straighter than chrysotile, and when examined under a polarized light microscope, they appear long and thin, almost needle-like. They are naturally found in bundles and are extremely brittle.
They can sometimes take the shape of grains or flat prisms. The fibers are flexible and they can be easily bent into a wide arch. However, excessive stress will cause the arch to snap and break into fibers of very small diameter, which can be inhaled.
The fibers have a flat end, and unlike chrysotile, it is not frayed or split. They are extremely acid-resistant and do not conduct electricity.
How was Amosite Asbestos Used?
The most significant uses of this type of asbestos were in thermal insulation, as an additive to strengthen cement, and in some roofing products. According to EMSL Analytical, Inc, an asbestos testing laboratory, the following list contains some additional commercial uses:
- Acid storage battery casings
- Spray on Insulation
- Ceiling tiles
- Asbestos reinforced plastics
- Pipe and Boiler insulation
- Transite Paneling – along with chrysotile and crocidolite
Asbestos ceiling tiles were commonly used in governmental buildings and schools, and can still be found in many older structures.
The biggest danger posed by amosite-containing building products is during removal. The brittle nature of the fibers causes this type of asbestos to be very friable, meaning it crumbles easily when touched. When the fiber bundles break, the fibers become airborne and remain in the air to be breathed in.
Research Shows that Amosite Asbestos Remains for a Very Long Time Inside the Lungs
In an article titled Biopersistence of Synthetic Vitreous Fibers and Amosite Asbestos in the Rat Lung Following Inhalation, published August 1998 in Toxicology and Applied Pharmacology, researchers measured amosite asbestos’ biopersistence, meaning how quickly amosite was cleared from the lungs through the body’s own natural defense mechanisms.
The scientists studied rats that inhaled amosite asbestos for five days during one full year after they had been exposed. The rats were exposed to fibers that were dispensed through aerosols that contained 150–230 fibers per cubic centimeter of air. Each of the dispensed fibers was longer than 20 micrometers.
After one year, the researchers observed that 27 percent of these fibers had remained in the rats’ lungs. They also observed that it took more than 400 days for the rats’ lung to clear any of the amosite fibers. These results led the researchers to conclude that the biopersistence of these amosite fibers made them carcinogenic.