This is a huge, robust crystal of the extremely rare manganese and boron-containing mineral, Gaudefroyite. The best crystals in the world for shape and symmetry came from only a few finds in this mine and others nearby, in the Kalahari Manganese Fields, in the 1980s. Superb, textbook single crystals like this, as thick and complete as this is (1 cm or so), are very rare. The symmetry and jet-black color combine, making this a dramatic competitive example of the species.