JacobsiteNamed in 1869 after the mine in Finland where it was first identified (a place known as the
JacobsiteNamed in 1869 after the mine in Finland where it was first identified (a place known as the type locality) this dark crust (measuring 3.8 x 3.5 x 3.2 cm) is a manganese iron oxide, formed during metamorphism of manganese deposits and as a primary mineral in lavas. It forms a solid solution series with the iron oxide magnetite with one metallic ion substituting for another freely in the crystal structure with the final composition along the continuum reflecting that of the initial magma or metamorphosed rock. Colour is black and it weighs in at 6 on Mohs hardness scale. This specimen was mined in South Africa, at the famous N'Chwaning II Mine in the Kalahari Manganese Field and displays sharp black octahedral crystals. LozImage credit: Rob Lavinsky/iRocks.comhttps://www.mindat.org/min-2061.htmlhttp://bit.ly/2zFqkFY -- source link
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