Tourmaline (variety Schorl), Erongo, Namibia

The Erongo Mountains in Namibia have yielded many impressive minerals with black tourmaline (variety schorl) almost being ubiquitous with all of them. Although typically serving as a backdrop to flashier Erongo minerals like aquamarine, sometimes schorl steals the show itself. I am particularly found of specimens like this one, showing significant natural etching of the schorl crystals. This occurs after the schorl has grown a complete crystal but, later, chemical conditions alter and become acidic to the schorl. The acidity etches the schorl but does not completely eradicate it, leaving an appealing form that tells a geologic story. Interestingly, not all of the schorls are etched as some of the smaller crystals reveal sharp terminations. Perhaps these are a new growth of schorl crystals after the acidic conditions departed? There is minor white feldspar and hyalite opal attached the base, with the hyalite only visible during exposure to long wave ultraviolet light (turns bright green). Ex George Sutherland collection. From Erongo Mountains, near Erongo, Namibia. Dimensions: 9 cm x 10 cm