A triclinic hydrous silicate of calcium occurring as minute needle- or blade-shaped crystals of a whitish colour in vesicles in eruptive rocks. Compare "dysclasite". Also: the mineral wollastonite, misidentified as a form of okenite (rare, now historical).
Early 19th century; earliest use found in Edinburgh New Philosophical Journal. From German Okenit from the name of Lorenz Oken, German naturalist + -it.