Manganese deposit, Ilfeld, Nordhausen, Harz, Thuringia, Germany

Mn³⁺O(OH)

Crystal System: monoclinic
Colour: gray-black, black
Lustre: resinous, sub-metallic, dull
Habitus: prismatic crystals. Also as stalactitic, botryoidal or granular aggregates.
Hardness: 4
Fracture: splintery
Cleavage: {010} perfect; {110} and {001} good
Density: 4.38 g/cm³ 
Origin and geological occurrence: it occurs in low-T hydrothermal veins or in sedimentary deposits.

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Smorf link

Samples:

4.24 Manganite Grey-black concretions of manganite. #economic minerals