Minerals from the Kalahari manganese fields of South Africa have become almost impossible to get hold of since the mine owners clamped down and forbade the miners to remove specimens. This is from the Nchwaning II mine.
Braunite is a silicate mineral containing both di- and tri-valent manganese with the chemical formula: Mn²⁺Mn³⁺₆[O₈|SiO₄]. Common impurities include iron, calcium, boron, barium, titanium, aluminium, and magnesium. Braunite forms grey/black tetragonal crystals and has a Mohs hardness of 6 – 6.5.
| Weight | 0.02 kg |
|---|---|
| Dimensions | 4 × 2.1 × 1.5 cm |