Tsumcorite (w. goethite and mimetite)

dolomite; goethite; mimetite

dolomite; goethite; mimetite

A matrix of siliceous dolostone hosts a shallow vug lined with grey-black micro-botryoidal goethite which is in turn extensively encrusted with elongated, orange-yellow crystals of tsumcorite (to 2 mm). Two radiating sprays (to 5 mm) and numerous individual tapered, needle-like crystals (to 3 mm) of very pale yellow mimetite are also present. The paragenesis appears to be: goethite >> tsumcorite >> mimetite. It is noted, however, that a few minute spherules of second generation (?) goethite have formed on the tsumcorite crystals.

Although no record is preserved with the specimen it is almost certainly from the second oxidation zone. It was formerly in the collection of Helmut Heuser (Germany) and was purchased from Ian Bruce (Crystal Classics).