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Calcite, (w. Minium and Mottramite)


Chemistry: CaCO3
Size: 80 mm
Owner: Mariusz Oleszczuk
Photographer: Mariusz Oleszczuk

Modified rhombohedrons of calcite (to 20 mm) on a matrix of very dark, grey-green, botryoidal mottramite (XRD confirmed).  Most, but not all of the calcite rhombs are flattened - some of them are almost lenticular in shape - while a few are steeply rhombohedral (Photographs 2 and 3; FOV 20 mm and 30 mm respectively).

Similarly most, but not all, of the calcites are richly included by minium (EDS confirmed) with a dense, brick-red colouration as a result; a minority, however, are either free of inclusions or sparsely included, and either colourless, or with a red tinge. This combination of habits, and of colourless, partly coloured, and intensely coloured calcites, set against the grey-green mottramite provides a very aesthetic colour contrast.  It is noted that the red colouration of the calcite was originally assumed to be due to included hematite.

Unfortunately the location in the mine from which this specimen was recovered is not recorded.