Cuspidine is a fluorine bearing calcium silicate mineral (sorosilicate) with formula: Ca4(Si2O7)(F,OH)2.

[2] Cuspidine occurs as crystals in tuff from Monte Somma.

In the Franklin, New Jersey mine area it occurs in contact metamorphosed limestone.

In Dupezeh Mountain, Iraq, it occurs in melilite bearing skarn.

Associated minerals include augite, hornblende, diopside, grossular, biotite, phlogopite, monticellite, wollastonite, calcite, spinel, magnetite and perovskite.