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RM1124   Sphalerite pseudom. after wurtzite, with plumbogummite and franckeite

San José mine, Ciudad de Oruro, Cercado, Oruro, Bolivia

Group of interpenetrated crystals of hexagonal shape, with a dark gray metallic color and brilliant luster. Crystals of this specimen remind wurtzite for its hexagonal shape and dipyramids observed. Many similar samples from this mine has been classified as wurtzite. For this reason we heve proceeded to analyze them. The results indicate that this is a really amazing and interesting pseudomorphosis of sphalerite after wurtzite. Accompanied by nice brilliant franckeite globular crystal aggregates and small hexagonal prism of plumbogummite (also a pseudomorph). A great opportunity for psedomorph and Bolivian mineral collectors.

Studies were carried on by X-ray diffraction of the matrix and hexagonal crystals. They have shown that it is sphalerite. Also, the Raman spectra shows that in the innermost areas of the crystals wurtzite presence has been detected, the rest is sphalerite. SEM-EDS yield a composition:  (Zn1.05,Fe0.09)Σ=1.14S1.00.

Specimens of well developed wurtzite are unusual. This hexagonal zinc sulphide, with some iron, presents dimorphism with sphalerite. It is known that wurtzite is stable at high temperatures, low temperatures being the most stable phase sphalerite. This Bolivian mine is the type locality for the wurtzite. We will send the analysis reports to the specimen buyer.

Size: 7.3 x 5.2 x 3.6 cm.
Main crystal: 18 x 16 mm.

Analyzed specimen with report