A mineral occurring typically as brownish fibrous crystals in some metamorphic rocks. It is a magnesium-rich iron silicate of the amphibole group.‘Accessory chlorite, magnetite or ilmenite, titanite, apatite, partly chloritized biotite, epidote, pyrite and sometimes cummingtonite, are present.’
- ‘This rock is a dark gray schistose rock containing radiating aggregates of cummingtonite and occasionally pyrrhotite.’
- ‘The two minerals can have similar distinctive brown colors and are hard to differentiate from each other, although cummingtonite is typically darker and slightly denser.’
Early 19th century named after Cummington, a town in Massachusetts, US, + -ite.
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