Prehnite is a calcium and aluminium inosilicate. Prehnite occurs as aggregates of stalactitic or botryoidal crystals in the orthorhombic crystal system, with only the crests of tiny crystals displaying any faces, which are nearly invariably bent or composite. It will very infrequently produce definite, well-defined crystals with a square-like cross-section, as those discovered at the Jeffrey Mine in Asbestos, Quebec, Canada. It has a vitreous to pearly sheen, a brittle fracture, and an uneven fracture. It ranges in hue from light green to yellow, as well as being colourless, blue, or white, and its hardness is 6-6.5.