Prehnite is an inosilicate of calcium and aluminium. Prehnite crystallizes in the orthorhombic crystal system, and most often forms as stalactitic or botryoidal aggregates, with only just the crests of small crystals showing any faces, which are almost always curved or composite. Very rarely will it form distinct, well-individualized crystals showing a square-like cross-section, including those found at the Jeffrey Mine in Asbestos, Quebec, Canada. Prehnite is brittle with an uneven fracture and a vitreous to pearly luster. Its color varies from light green to yellow, but also colorless or white. In April 2000, rare orange Prehnite was discovered in the Kalahari Manganese Fields, South Africa. Prehnite is mostly translucent, and rarely transparent. It was first described in 1788 for an occurrence in the Karoo dolerites of Cradock, South Africa and named for Colonel Hendrik Von Prehn, commander of the military forces of the Dutch colony at the Cape of Good Hope. Extensive deposits of gem-quality Prehnite occur in the basalt tableland surrounding Wave Hill Station in the central Northern Territory, of Australia.