Sulphide, wurtzite group. Wurtzite, which is trigonal or hexagonal, is the high temperature paramorph of sphalerite, which is isometric; the transition for pure ZnS occurs at 1020oC, and this transition temperature is lowered by the presence of iron in solid solution ( AM 46.1382).
Specific gravity: 4 to 4.1
Hardness: 3½ to 4
Colour: Dark reddish-brown to black, orange-brown
Common impurities: Fe,Cd
Wurtzite is of hydrothermal origin in veins with other sulphides (Webmin, HOM), also along shrinkage fractures
in siderite concretions, of low-temperature origin. Associated
minerals include sphalerite, pyrite,
chalcopyrite, baryte and
Chalcopyrite is an epitaxial mineral (Mindat).
The type locality is the San José Mine, Oruro City, Cercado Province, Oruro, Bolivia.
At Llallagua, Rafael Bustillo, Potosí, Bolivia, wurtzite forms interlaminations in marcasite/pyrite, and replacements of pyrrhotite, associated with galena and franckeite and a carbonate (siderite or rhodochrosite). In vugs wurtzite forms crystals to 2 cm, sometimes associated with sphalerite, wolframite and franckeite, but most wurtzite crystals have inverted to sphalerite. Fibrous wurtzite occurs in some veins as coatings on sphalerite; crystals on marcasite have been found, and also fine crystals associated with franckeite, wavellite and vauxite (Minrec 37.2.159-160).
At the Francon Quarry, Montreal, Quebe, Canada, a single crystal of wurtzite has been found associated with quartz, calcite and baryte (Minrec 37.1.55).
At Huinac, Ancash department, Peru, wurtzite is accompanied by rhodochrosite (Minrec 42.2.148)
At Pachapaqui, Ancash department, Peru, wurtzite is associated with quartz; there is no evidence of rhodochrosite (Minrec 42.2.150).
At the Palitra pegmatite, Lovozero Massif, Murmansk Oblast, Russia, wurtzite occurs as crystal clusters to 1 mm on ussingite and sodalite .
Near Shelocta, Pennsylvania, USA, wurtzite occurs in siderite concretions. Three new paramorphs of zinc sulfide have been described. The zinc sulfide paramorphs occur along fractures in the concretions and generally are embedded in baryte. Other associated minerals include calcite, chalcopyrite, pyrite and sphalerite. Sphalerite is found to have formed later than the wurtzite (AM 35.29-42).
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