Dolomite, (after Calcite)

Size: 97 mm
Owner: Mariusz Oleszczuk
Photographer: Mariusz Oleszczuk

A shell-like "cast" of off-white, slightly pinkish, crystallised dolomite bearing the molds of the crystals over which it originally formed - probably calcite (?), although the precursor mineral has subsequently dissolved away. Both sides of the specimen are shown (photographs 1 and 2).

One side of the cast (Photograph 1) is richly encrusted with tiny sub-spherical aggregates of a green mineral originally identified as mottramite, but subsequently confirmed as conichalcite (EDS verified).  Apparently post-dating the conichalcite are sparse, finger-like groups of silver-grey coronadite (to 12 mm; also EDS confirmed), at least some of which are hollow (see Photograph 3; FOV c. 30 mm). 

The other side of the specimen (Photograph 2) is very different in appearance.  This surface shows idiomorphic molds of the calcite (?) druse over which the dolomite crystallised, and the coverage of conichalcite and coronadite is very much more sparse.  Here, the conichalcite occurs mainly as isolated olive-green spheres (sub-mm), and there are only one or two tiny tube-like structures of coronadite.  Note also the chatoyant surfaces of the dolomite, caused by the parallel alignment of the crystallites that comprise the "shell".

The specimen was formerly in the collection of Jim Robison (USA).