Mineral: Goethite, Smithsonite
Chemistry: FeO(OH)
Size: 60 mm
Owner: Chris Amo
Photographer: John Schneider

Goethite is a common mineral at Tsumeb, although it seldom forms attractive specimens in its own right.

On this specimen, a coating of goethite has formed over rhombohedral crystals of smithsonite, thickening in places to form attractive botryoidal textures.

Visually similar coatings (over either calcite or smithsonite rhombs) are sometimes labelled as heterogenite.  However, cobalt is a relatively scarce element at Tsumeb, and analytical confirmation is required to differentiate these two minerals, of which goethite is by far the more common.