Calcite, (w. Cuprite and Malachite)

Chemistry: CaCO3
Size: 70 mm
Owner: Geoff Krasnov
Photographer: Geoff Krasnov

A very colourful calcite specimen, with a complex paragenesis.

The first generation of calcite comprises a layer of intergrown crystals extensively coloured blue-green by minute inclusions of dioptase, and partly overgrown by an earthy apple-green crust of duftite/conichalcite (?). This layer is visible at the bottom-left of the main photograph, and further detail can be seen in Photograph 2 (FOV c. 30 mm).     

The second calcite generation consists of sharp rhombohedral crystals (to 10 mm).  The cores of these crystals are coloured bright orange-red by tiny inclusions of cuprite (v. chalcotrichite), while the narrow outer zones of the calcite more-or-less colourless and transparent.  However, these colourless outer zones are included by aggregates of acicular, lustrous green malachite, many of which display a "bow-tie" habit.  Typically, the malachite aggregates are only partly enclosed in the calcite, with the green fibrous aggregates protruding from many of the calcite faces.

The specimen was formerly in the collection of Rob Smith (South Africa).