Home > African Minerals – April 25 > MS1185 Wurtzite

Wurtzite


Wurtzite is simple zinc sulfide, sharing the same chemistry as sphalerite, but crystallizing with hexagonal symmetry. Under room conditions, sphalerite is the stable form of zinc sulfide, while at high temperatures wurtzite is more stable. As such, wurtzite is a bit of a mineral oddity. Friedel (1861) distinguished the mineral from sphalerite, naming the species after Charles Adolphe Wurtz (1817-1884), a French chemist. While found in many ore deposits, wurtzite is significantly (hundreds or thousands of times) rarer than sphalerite. Until this discovery in Tanzania, large wurtzite crystal were known primarilly from Bolivia. Bolivian specimens are typically convulted platy aggregates, indistinctly formed, and nearly black.

The tanzanite mines stunned the mineral collecting community first in 2009 with fist-sized geodesic pyrite crystals, and later in 2011-2013 with quantities of fine wurtzite and alabandite crystals. Single crystal X-ray diffraction identifies this wurtzite as the 4H polytype (RRUFF R130069). The label accompanying this specimen reads "wurtzite-4H". Large and sharp wurtzite crystals from the tanzanite mines, such as this fine example, have set new world standards for the species. This is a large orange-brown partial crystal, showing 4 of 6 prism faces and two pedial forms. The crystal is approximately 65% complete. There is minor chattering along the crystal edges, likely a consequence of the mining methods. The color is a rich orange-brown and luster is subadamantine. The color and luster are both excellent for this find, and this example is sharper and larger than most.

Price: $800

Item code: MS1185

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