Ca₆(Fe,Al,Mn)₂SO₄[B(OH)₄](OH)₁₂.25H₂O

This sample of sturmanite is displayed in the Smithsonian Museum of Natural History. Sturmanite is a sulphate mineral which contains boron. It has the composition Ca₆(Fe,Al,Mn)₂SO₄[B(OH)₄](OH)₁₂.25H₂O. This sample is about 3 cm wide and is from N'Chwaning mine, Hotazel, Cape Province, South Africa.