Cummingtonite

Cummingtonite was named after the town of Cummington, Massachusetts, where it was discovered in 1824. It is also found in Sweden, South Africa, Scotland, and New Zealand. ==Chemistry==

Cummingtonite is a member of the cummingtonite-grunerite solid solution series which ranges from for magnesiocummingtonite to the iron rich grunerite endmember . Cummingtonite is used to describe minerals of this formula with between 30 and 70 per cent . Thus, cummingtonite is the series intermediate. Manganese also substitutes for ) within cummingtonite amphibole, replacing B site atoms. These minerals are found in high-grade metamorphic banded iron formation and form a compositional series between (tirodite) and (dannemorite). Calcium, sodium and potassium concentrations in cummingtonite are low. Cummingtonite tends toward more calcium substitution than related anthophyllite. Similarly, cummingtonite has lower ferric iron and aluminium than anthophyllite. Amosite is a rare asbestiform variety of grunerite that was mined as asbestos only in the eastern part of the Transvaal Province of South Africa. The origin of the name is Amosa, the acronym for the mining company "Asbestos Mines of South Africa". ==Occurrence==

Cummingtonite is commonly found in metamorphosed magnesium-rich rocks and occurs in amphibolites. Usually it coexists with hornblende or actinolite, magnesium clinochlore chlorite, talc, serpentine-antigorite minerals or metamorphic pyroxene. Magnesium-rich cummingtonite can also coexist with anthophyllite. Cummingtonite has also been found in some felsic volcanic rocks such as dacites. Manganese rich species can be found in metamorphosed Mn-rich rock units. The grunerite end member is characteristic of the metamorphosed iron formations of the Lake Superior region and the Labrador Trough. With prograde metamorphism cummingtonite and grunerite morph to members of the olivine and pyroxene series. ==References==