N'Chwaning II Mine, N'Chwaning Mines, Kuruman, Kalahari manganese fields, Northern Cape Province, South Africa
Cabinet, 9.8 x 5.9 x 4.9 cm
This mineral was only identified and named in 2007. It had previously been identified as poldervaartite, with which it is almost identical in formula, but olmiite contains more Mn than poldervaartite. This cluster, sandwiched by a manganese and iron-rich matrix, measures a very impressive 6 cm in length by 2.5 cm at its widest point.