Jacobsite

General
Category| Oxide minerals
Spinel group
Spinel structural group
Formula| 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 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]

## References

[edit]

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

* National Pollutant Inventory - Manganese and compounds Fact Sheet

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Manganese minerals

Borates|

* Sussexite
* Tusionite

Carbonates|

* Ankerite
* Kutnohorite
* Rhodochrosite
* Manganoan calcite

Oxides|

| Simple|

* Hausmannite
* Manganite
* Manganosite
* Nsutite
* Pyrolusite

|

Mixed|

* Birnessite
* Bixbyite
* Ferrocolumbite
* Ferrotantalite
* Galaxite
* Jacobsite
* Manganotantalite
* Psilomelane (calvonigrite)
* Romanèchite
* Tantalite
* Todorokite
* Umber

Phosphates|

* Childrenite
* Graftonite
* Lithiophilite
* Natrophilite
* Purpurite
* Triplite
* Triploidite
* Zanazziite

Silicates|

* Babingtonite
* Braunite
* Brownleeite
* Calderite
* Chloritoid
* Eudialyte
* Glaucochroite
* Jeffersonite
* Knebelite
* Ottrelite
* Piemontite
* Pyroxferroite
* Rhodonite
* Spessartine
* Sugilite
* Tephroite
* Zakharovite
* Zircophyllite

Sulfides|

* Alabandite
* Hauerite
* Rambergite

Other|

* Axinite (borosilicate)
* Geigerite (arsenate)
* Manganese nodule (various)
* Samsonite (sulfosalt)
* Zincobotryogen (sulfate)
* Wolframite (tungstate)
* Hübnerite (tungstate)

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