Definition of cummingtonite in English:



mass noun
  • 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.