Chemistry: CaCO3
Size: 95 mm
Owner: Harvard University (Karabacek Collection)
Photographer: Malcolm Southwood

Vitreous, snow-white, club-shaped crystals of aragonite (to 19 mm) on a cavernous matrix of anidiomorphic casts of pale-green zincian (?) dolomite (?). Under the microscope some small but attractive spherulitic rosasites are visible.


This specimen is #4008 in the Karabacek Collection, which dates it to the first oxidation zone, and #93441 in the MGMH Catalogue.


The accompanying labels identify this specimen as "nicholsonite", the zinc-bearing varietal of aragonite.  There is no indication that the chemistry of the specimen has been determined, however, and the habit and colour of the crystals would be more consistent with the lead-bearing varietal, "tarnowitzite".



Courtesy  of  the  Mineralogical  &  Geological  Museum  at  Harvard  University, Aragonite; MGMH  ID# 93441, Tsumeb; Namibia. @ copyright 2012, President and Fellows of Harvard College. All rights reserved.