Dioptase on plancheite
description: LOCALITY: Pimbi, Katanga Province, Democratic Republic of the Congo 6" across Ex collections of Ed David and the late John F Barlow. The things that put this piece ahead of other Congo dioptase: (a) The overall size of this piece is impressive. When I was trawling for dioptase in Katanga province in 2009, the largest matrix pieces recovered were only 4" across and of inferior quality. (b) The crystals are separated from each other so the crystal shapes are easier to appreciate. Most dioptase from the Congo, and other localities, consist of druses of dioptase crystals which are not separated. Such specimens are not nearly as esthetic. (c) The dioptase crystals on this specimen are gemmy and lustrous - not the norm which is opaque and dull. (d) The matrix of this specimen is attractive and unusual. It is a felt textured, somewhat botryoidal blue mineral which I believe to be plancheite. Katanga province is the only place that gives rise to this attractive mineral combination. Unlike most other worldwide dioptase specimens, the dioptase crystals are set on a matrix which is much more attractive than a rocky brown matrix - which is the norm even with Tsumeb dioptase. Although Tsumeb is universally regarded as the best dioptase locality on earth, this piece would fit in any upper to top level collection of esthetic dioptase specimens. The crystal morphology distinguishes Katanga dioptase from Tsumeb dioptase. Pimbi dioptase is typically elongated along the c-axis although I have not seen crystals with this distinct morphology from production since 2000. The specimen was reinforced by Cal Graeber. It has been soaked in a water soluble glue to ensure physical stability since this specimen is relatively thin.

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