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CategoryOxide minerals
Spinel group
Spinel structural group
(repeating unit)
iron(II,III) manganese oxide, (Mn,Mg)Fe2O4
IMA symbolJcb[1]
Strunz classification4.BB.05
Crystal systemIsometric
Crystal classHexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space groupFd3m (no. 227)
Unit cella = 8.457 Å; Z = 8
ColorBlack to brownish black
Crystal habitDisseminated to massive, rarely as octahedral crystals
TwinningSpinel law, flattened on {111} or lamellar
Cleavage{111}, probably a parting
Mohs scale hardness5.5–6.5
Streakreddish black to brown
Specific gravity4.76
Optical propertiesIsotropic
Refractive index~2.3
Other characteristicsweakly magnetic

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]

Jacobsite, N'Chwaning Mines, Kuruman, Kalahari manganese fields, Northern Cape Province, South Africa. Size 3.8 x 3.5 x 3.2 cm

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]


  1. ^ 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.
  2. ^ a b c Handbook of Mineralogy
  3. ^ a b Mindat.org
  4. ^ a b Webmineral data