“Amosite” is not a true mineral name. It stands for asbestos mines of South Africa. Amosite is the fibrous form of amphiboles in the Cummingtonite-Grunerite solid solution series. Amosite is sometimes called brown asbestos. After chrysotile it is the 2nd most common type of asbestos.  The most common amphibole is hornblende and if it was fibrous it would be considered ‘amosite.’ It is commonly used in boiler and pipe insulation. It has been known to be used in nearly a pure form as a blown on sound proofing in buildings like movie theaters.

Crocidolite is the fibrous form of Riebeckite amphibole and is sometimes called blue asbestos. It is less common than amosite in lab submitted samples. It is the type of asbestos most chemically resistant to acids and has been used as a filtering agent. It was once used in the filters of Kent cigarettes. In lab samples it is most often seen in cement asbestos pipe and magnesium block insulation.

Amphiboles are a large group of structurally similar hydrated double chain silicate minerals with varying amounts of sodium, calcium, mangnesium, iron, and aluminum. These ‘garbage can’ minerals have highly variable compositions even in the same mineral name. Tremolite and Actinolite belong to the same solid solution series in which Actinolite contains more iron and Tremolite contains more magnesium. Winchite, the amphibole fiber associated with vermiculite deposits from Libby Montana, is not part of the same solid solution series as tremolite-actinolite but can form solid solution mixtures with them. Winchite is more sodium and calcium rich than the Tremolite-Actinolite series amphiboles. Winchite may be reported as Actinolite by some labs as its optical properties are similar. Since the distinction between Winchite and Actinolite cannot be reliably made by standard PLM analysis, and since no one

has proven that Winchite is not also a health hazard, the distinction as to whether it is or isn’t a regulated material is probably moot. Data collected by the EPA in regard to health effects on persons living in Libby, Montana does not show that Winchite is any less of a health hazard than Actinolite and Tremolite. Common sense suggests all fibrous amphiboles should be considered a health hazard and treated as regulated asbestos until there is conclusive evidence to show otherwise. Scientists don’t always agree on what is or isn’t the fibrous forms of these minerals either. Epidemiologists may define a fiber as having a length to width ratio of 3:1 but a geologist has been trained to say 20:1 is the minimum to consider a mineral ‘asbestiform’ and asbestos minerals would be more likely to have length to width rations of 100:1.  The hazard is all about the ability of asbestos to break up into ‘zillions’ of fine fibers with fiber dimensions that cause problems in the lungs. The problem with using the 3:1 fiber definition is that common hornblende, which is pretty ubiquitous as a rock forming mineral, often has a growth habit that exceeds that ratio!