Jacobsite
(repeating unit)iron(II,III) manganese oxide, (Mn,Mg)Fe2O4 IMA symbol Jcb[1] Strunz classification 4.BB.05 Crystal system Isometric Crystal class Hexoctahedral (m3m)
H-M symbol: (4/m 3 2/m) Space group Fd3m (no. 227) Unit cell a = 8.457 Å; Z = 8 Identification Color Black to brownish black Crystal habit Disseminated to massive, rarely as octahedral crystals Twinning Spinel law, flattened on {111} or lamellar Cleavage {111}, probably a parting Fracture Conchoidal Mohs scale hardness 5.5–6.5 Luster Metallic Streak reddish black to brown Diaphaneity Opaque Specific gravity 4.76 Optical properties Isotropic Refractive index ~2.3 Other characteristics weakly magnetic References [2][3] 
Jacobsite, N'Chwaning Mines, Kuruman, Kalahari manganese fields, Northern Cape Province, South Africa. Size 3.8 x 3.5 x 3.2 cm
H-M symbol: (4/m 3 2/m)
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 (Mn,Mg)Fe2O4 or with oxidation states and substitutions: (Mn2+,Fe2+,Mg)(Fe3+,Mn3+)2O4.[2][4]
It occurs as a primary phase or as alteration of other manganese minerals during metamorphism of manganese deposits.[4] Typical associated minerals include hausmannite, galaxite, braunite, pyrolusite, coronadite, hematite and magnetite.[2] It is a ferrimagnetic substance, which is weakly attracted by a magnet.
It was first described in 1869 and named for the Jakobsberg Mine, Nordmark, Filipstad, Värmland, Sweden.[3]
References
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ a b c Handbook of Mineralogy
- ^ a b Mindat.org
- ^ a b Webmineral data
- National Pollutant Inventory - Manganese and compounds Fact Sheet
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