Prehnite, an inosilicate composed of calcium and aluminium, exhibits crystallization within the orthorhombic crystal system. Typically, it takes on formations such as stalactitic, botryoidal, reniform, or globular aggregates. The surfaces of small crystals often reveal curved or composite faces, with distinct, well-individualized crystals presenting a square-like cross-section being a rare occurrence, as observed in the Jeffrey Mine in Asbestos, Quebec. Prehnite displays brittleness, an uneven fracture, and a luster ranging from pearly to vitreous.
Its color spectrum spans from light green to yellow, and it can also manifest as colorless, blue, pink, or white. A notable discovery in April 2000 revealed rare orange prehnite in the Kalahari Manganese Fields of South Africa. Despite not being classified as a zeolite, prehnite is commonly found in association with minerals like calcite, datolite, apophyllite, laumontite, stilbite, and heulandite. These occurrences typically take place in veins and cavities of basaltic rocks, and occasionally in gneisses, granites, and syenites.
