Jacobsite and Calcite

Jacobsite is in the spinel group and forms a solid solution series with magnetite. Thus, it is slightly magnetic. This specimen has hundreds of isometric crystals coating shards of manganese rich matrix. Curiously, small isolated mounds of tiny scalenohedral calcites add contrast. Close inspection reveals tan rectangular crystals which I suspect are bulfontenites. Great piece for a KMF collector. Ex Martin Zinn thumbnail collection which notes he paid $160 for it in 2002.

Locality: Nchwaning 2 Mine, Kalahari Manganese Fields, Near Kuruman South Africa

Composition: Manganese Iron Oxide