What is "jacobsite"

n. (context mineralogy English) A manganese iron oxide mineral, a magnetite spinel.

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 MnFeO or with oxidation states and substitutions: (Mn,Fe,Mg)(Fe,Mn)O.

It occurs as a primary phase or as alteration of other manganese minerals during metamorphism of manganese deposits. Typical associated minerals include hausmannite, galaxite, braunite, pyrolusite, coronadite, hematite and magnetite.

It was first described in 1869 and named for the Jakobsberg Mine, Nordmark, Filipstad, Värmland, Sweden.