Cummingtonite

Cummingtonite is an iron- and magnesium-bearing amphibole mineral found mainly in metamorphic rocks. Its name comes from Cummington, Massachusetts, where it was first described.

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Amphibole: A group of inosilicate minerals built from double chains of silica tetrahedra. Cummingtonite belongs to this mineral group and shares its characteristic double-chain structure.
Double-chain silicate: A silicate structure made of two linked chains of silica tetrahedra. These linked chains form cummingtonite’s defining amphibole framework.
Metamorphic petrology: The study of rocks transformed by changes in pressure, temperature, and chemical environment. Cummingtonite is interpreted as part of metamorphic mineral assemblages.
Cummington, Massachusetts: A town in western Massachusetts in the United States. The mineral was named for this town, where it was first described.
Anthophyllite: An orthorhombic amphibole with compositionally variable magnesium and iron. It shares cummingtonite’s crystal system but differs in structure and mineral-series relations.
Inosilicate: A silicate mineral whose structure contains chains of linked silica tetrahedra. Cummingtonite’s double chains place it within this broader structural class.
Solid solution: A crystalline phase in which elements substitute for one another within a shared structure. Iron and magnesium substitute across cummingtonite’s compositional range.
Metamorphic index mineral: A mineral whose presence helps constrain the pressure and temperature conditions of metamorphism. Its occurrence can help constrain conditions when considered with its associated minerals.
James Dwight Dana: An American geologist and mineralogist who authored influential works on mineral classification. Dana described cummingtonite in the nineteenth century and gave it its name.
Actinolite: A calcium-bearing amphibole ranging from magnesium-rich to iron-rich compositions. Its calcium-bearing chemistry distinguishes it from calcium-poor cummingtonite.