Dioptase

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Dioptase, a copper silicate species, is generally very rare in secondary copper deposits worldwide, but there are a number of exceptions, where it crystallizes as very well-formed glassy emerald-green crystals. Its Type Locality at Altyn-Tube in Kazakhstan is one such case, but there are several well-known deposits in Africa too, of which the famous Tsumeb mine is the best-known. In the Republic of Congo (Brazzaville), near Renéville incredibly rich, pure veins and nodules of Dioptase are lined with very well-crystallized glassy emerald-green Dioptase crystals. Generally speaking, the Dioptase crystals from Renéville are not quite as gemmy as those from Tsumeb, but for sheer wow-factor the richness of Renéville specimens is hard to beat. At 15 cm in length this is a really dramatic large display specimen and represents a lot of Dioptase for the price, with individual crystals reaching 7 mm in length and showing the classic rhombic prism form. The back of this plate of Dioptase is a complex series of hollow casts after an unknown mineral with massive to botryoidal pale blue Chrysocolla coating the inside of the casts. Ex Kessler Collection.