WurtziteA close cousin of the zinc sulphide sphalerite (seeon.fb.me/1GaU0GY), it shares the s

WurtziteA close cousin of the zinc sulphide sphalerite (seehttp://on.fb.me/1GaU0GY), it shares the same chemical formula but crystallises in a different structure, quite a common feature in the mineral world with the varied forms being known as polymorphs (from the Greek for many shapes). It has another unusual feature to its structure, known as hemimorphy (from the Greek for half shape) , in which there is no mirror image symmetry between top and bottom of the crystal, meaning that the top and bottom ends display different faces. The common form is a six sided prisms or plates often striated parallel to the base, and the usual colour a very dark reddish-orangey brown, often transparent in a strong fibre optic light. It is a soft mineral (3.5=4 on Mohs scale) and relatively dense. It was named in 1861 after a French chemist and is found in veins that have precipitated from metal rich hydrothermal fluids or as concretions in sedimentary rocks during the long arduous passage from sediment to stone.Famous localities include Germany, Bolivia, Peru, the USA though this specimen (measuring 1.6 x 1.1 x 0.5 cm) was found in the Merelani hills of Tanzania (also famed for this production of tanzanite and tsavorite garnet).LozImage credit: Marin Mineralshttp://www.galleries.com/Wurtzitehttp://www.mindat.org/min-4318.html -- source link

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