Minerals described in 1869

Jacobsite is a manganese iron oxide mineral. It is in the spinel group and forms a solid solution series with magnetite. The chemical formula is (Mn,Mg)Fe2O4 or with oxidation states and substitutions: (Mn2+,Fe2+,Mg)(Fe3+,Mn3+)2O4. thumb|left|Jacobsite, N'Chwaning Mines, Kuruman, Kalahari manganese fields, [[Northern Cape Province, South Africa. Size 3.8 x 3.5 x 3.2 cm]]