Wednesday, June 2, 2010

June 2010 Mineral of the Month


Prehnite is the first mineral ever to be named after a person, and was first described in 1789 for an occurrence in Haslach, Harzburg and Oberstein, Germany., It is 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. Prehnite is a member of the silicates family of minerals. It is brittle with an uneven fracture and a vitreous to pearly luster. 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 itself a zeolite, it is found associated with minerals such as datolite, calcite, apophyllite, stilbite, laumontite and heulandite. It occurs in veins and cavities of basaltic rocks and sometimes in granites and gneisses. 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. There are no commercial uses for Prehnite other than collecting, carving and jewelry making. This, of course, makes it the perfect lapidary material for rockhounds.