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.
Sturmanite is a rare sulfate mineral with the chemical formula Ca₆Fe³⁺₂(SO₄)2.5(OH)₁₂ · 25 H₂O. It crystallises in the tetragonal system and it has a Moh’s hardness of 2.5. Sturmanite has a bright yellow to amber colour and falls in the ettringite group