Thumbnail, 2.3 x 1.4 x 0.7 cm
Wessels Mine (Wessel's Mine), Hotazel, Kalahari manganese fields, Northern Cape Province, South Africa

A crust of super-bright yellow crystals of the rare (in crystals) mineral ettringite (Hydrated Calcium Aluminum Sulfate Hydroxide), which forms as a precipitate from hydrothermal solutions. It is best-known and has been found in its best specimens at this locality.