Formula: Ca8(Si2O7)2F4
Sorosilicate (Si2O7 groups), wöhlerite group
Specific gravity: 2.97 to 2.99
Hardness: 5 to 6
Streak: White
Colour: Colourless, tan, light brown, pale red.
Common impurities: Mn,Na,K,Cl

Metamorphic environments

Cuspidine is an uncommon sorosilicate. Associated minerals include augite, hornblende, diopside, grossular, biotite, phlogopite, monticellite, wollastonite, calcite, spinel, magnetite and perovskite (HOM, Dana).

At the Dupezeh Mountain, Iraq, cuspidine occurs in melilite skarn (HOM).

At the type locality, Monte Somma, Somma-Vesuvius Complex, Naples, Campania, Italy, cuspidine has been found in ejected masses (Webmin, HOM).

At Novinka, Yakutia, Russia, cuspidine has been found in a kimberlite pipe (Dana).

At Franklin, New Jersey, USA, cuspidine occurs in contact metamorphosed limestone (HOM). It is in apparent chemical equilibrium with glaucochroite, which is younger, and hardystonite, which is altered in some specimens to clinohedrite. Cuspidine also occurs, within assemblages of glaucochroite crystals, as a late-stage mineral, forming druses with clinohedrite in solution vugs in willemite (AM 72.423).

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