Prehnite is a inosilicate of calcium and aluminium with the formula: Ca2Al(AlSi3O10)(OH)2. Limited Fe3+ substitutes for aluminium in the structure. 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. It is brittle with an uneven fracture and a vitreous to pearly lustre. Its hardness is 6-6.5, its specific gravity is 2.80-2.90 and its color varies from light green to yellow, but also colorless, blue or white. It is mostly translucent, and rarely transparent.
Though not a zeolite, it is found associated with minerals such as datolite, calcite, apophyllite, stilbite, laumontite, heulandite etc. in veins and cavities of basaltic rocks, sometimes in granites, syenites, or gneisses. It is an indicator mineral of the prehnite-pumpellyite metamorphic facie.
It was first described in 1788 for an occurrence in the Karoo dolerites of Cradock, Eastern Cape Province, South Africa. It was named for Colonel Hendrik Von Prehn, commander of the military forces of the Dutch colony at the Cape of Good Hope from 1768 to 1780. Coinsidently being the first stone named after a person.
Extensive deposits of gem quality Prehnite occur in the basalt tableland surrounding Wave Hill Station in the central Northern Territory, of Australia within a small township called Kalkarindji located on the Buntine Highway. At the 2006 census, Kalkarindji had a population of 544.
Kalkarindji and the nearby settlement of Daguragu are the population centers of the land formerly held under the Wave Hill Cattle Station. In 1966, the indigenous station workers, led by Vincent Lingiari, staged a walk-off in protest against oppressive labor practices; The station occupies an area of 13,500 square kilometres (5,212 sq mi) and encompasses part of the Victoria River, which bisects the station. The country is a high open downs with basalt plains and covered in mitchell grass, well watered by the Victoria river and numerous creeks. Following this, much of the land was returned to the Gurindji people by UK-based station owners, The Vestey Group and the Australian Government in 1975.
Interactive Map of Kalkarindji
Stunning specimens and Gem Quality Prehnite has been fossicked from the Wave Hill region Since the 60’s but only recently has any commercial quality been won. This material is unique in colour and lustre and is by far superior to other locations in the world. It has a distinct quality that makes it the most attractive Prehnite currently available.