Cobaltoan Smithsonite on Tennantite - image 1

Cobaltoan Smithsonite on Tennantite

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This cabinet-sized specimen is a magnificent presentation of the well-known, but rare combination of Smithsonite coating perfect tetrahedral Tennantite crystals known from Tsumeb mine. The Tennantite crystals reach an impressive 3 cm on edge and are exceptionally well-formed - forming a bed of large intergrown tetrahedral crystals. The Smithsonite presents a pale pinkish colour, indicating that it is slightly cobaltoan, and is extremely well-crystallized but as very small crystals. These crystals form a complete, but relatively thin crust upon the Tennantite and could be described as epimorphous, but the Tennantite is still present underneath rather than as an epimorphic cast. The underside of the specimen is pure sulphosalt (Tennantite) and sulphide (Galena). The specimen presents superbly well with only slight damage to the tip of one of the tetrahedral crystals, with the internal Tennantite now showing through. It really is a marvellous example of this classic Tsumeb assemblage and has been hidden for generations within the Weyand collection in Tsumeb. On a technical note, Tennantite is now a subgroup rather than an indvidual species in its own right. We have not analysed this specimen, but it is generally accepted that the majority of Tsumeb specimens are the new species Tennantite-(Zn). This fits perfectly with the outer coating of Smithsonite - a zinc-bearing secondary species.