Formation
(1) Hydrothermal, through precipitation from late magmatic, low-temperature (usually < 200 °C) aqueous solutions in bubble spaces (amygdules) and fissures in mafic volcanic rocks.
(2) Metasomatic, in the course of low-grade metamorphism (zeolite facies) or retrograde alteration of calcium-rich rocks with the addition of fluorine and potassium ions.
