Chemical formula: (Mg2.1,Fe4.9)Si8O22(OH)2 - Fe7Si8O22(OH)2
Source: Predominant source is South Africa
Amosite (Grunerite) is also known as “brown asbestos”. It is the second most common asbestos type used (about 5% of asbestos found in building materials). Asbestiform grunerite is commercially known as Amosite due to one of its main sources, AMOSA (Asbestos Mines of South Africa). Its true mineralogical name is Grunerite.
Grunerite fibers are thicker and much straighter than chrysotile. The fibers have excellent acid resistance and are a non-conductor of electricity.
Its high iron content characterizes Amosite chemistry. Amosite is a member of the Cummingtonite - Grunerite solid solution and as such does not have a definite chemical formula; any particular occurance may have a composition anywhere within the grunerite range. Amosite asbestos is typically close to the Mg rich end member of grunerite but not so Mg rich that it would be classified as cummingtoite. Mn substitution exists with most Mn replacing Fe in the M4 structural site. Grunerite is a member of the amphibole double chain silicates.
By Polarized Light Microscopy (PLM) Amosite fibers tend to be thick and blocky but at times can also appear quite long and thin (needle like). Amosite is monoclinic and has a positive sign of elongation. It is typically non-pleochroic. The refractive indice ranges are 1.664-1.686 for a and 1.687-1.729 for ? and vary depending on the exact elemental composition. Random orientation SAED of Amosite shows a layerline spacing of 5.3 Å with twinning often present.
Acid storage battery casings
Spray on Insulation
Asbestos reinforced plastics
Pipe and Boiler insulation
Transite Paneling - along with chrysotile and crocidolite