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Black manganosite crystals with zincite and sonolite
Category Oxide mineral
(repeating unit)
Manganese oxide, MnO
Strunz classification 04.AB.25
Crystal system Cubic
Unit cell a = 4.44 Å; Z=4
Color Emerald-green, becoming black on exposure to air
Crystal habit Granular to massive; Octahedral crystals uncommon
Crystal symmetry Isometric hexoctahedral
H-M symbol: (4/m32/m)
Space group: F m3m
Cleavage Perfect on [100], [010] and [001]
Fracture Fibrous
Mohs scale hardness 5 - 6
Luster Vitreous, adamantine to dull
Streak Brown
Diaphaneity Transparent to translucent
Specific gravity 5.364
Optical properties Isotropic
Refractive index n = 2.16–2.17
References [1][2][3]

Manganosite is a rare mineral composed of manganese(II) oxide MnO. It was first described in 1817 for an occurrence in the Harz Mountains, Saxony-Anhalt, Germany.[2] It has also been reported from Langban and Nordmark, Sweden and at Franklin Furnace, New Jersey. It also occurs in Japan, Kyrgyzstan and Burkina Faso.[3]

It occurs in manganese nodules. It also occurs as alteration of manganese minerals such as rhodocrosite during low oxygen metamorphism and metasomatism.[3]