Cylindrite with Franckeite and Wurtzite

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Cylindrite is a fascinating mineral species, bizarre in possessing a unique cylindrical crystal habit, and with an equally unusual composition: combining lead, tin, iron, antimony and sulphur. Perhaps unsurprisingly, it is not found in many places worldwide with all of the notable occurrences in Bolivia in South America. This very rich large miniature specimen comes from the San Francisco mine near the town of Poopó, with several other mines in this region known for great Cylindrite crystals. There are several distinctive features to this specimen, firstly, with the association of brown Wurtzite filling many of the spaces between the long Cylindrite crystals, and the very rare species Franckeite filling the other gaps. However, it is only really the Cylindrite on this piece that is really well crystallized. The Cylindrite is distributed throughout the whole sample, but with one area showing a prominent fan-like spray, with crystals reaching over 2 cm in length. Internally, particularly well seen along the edges of the specimen, the Cylindrite crystals are made up of concentric layers with the core occasionally falling away to make slightly tubular crystals. A great sample of this unusual sulphosalt species. Ex David Hardman Collection, no. 1631.