Jacobsite
| Jacobsite | |
|---|---|
 |
|
| General | |
| Category |
Oxide minerals Spinel group Spinel structural group |
|
Formula (repeating unit) |
iron(II,III) manganese oxide, MnFe2O4 |
| Strunz classification | 4.BB.05 |
| Crystal system | Isometric |
| Crystal class | Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m) |
| Space group | Fd3m |
| 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 | |
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 MnFe2O4 or with oxidation states and substitutions: (Mn2+,Fe2+,Mg)(Fe3+,Mn3+)2O4.
It occurs as a primary phase or as alteration of other manganese minerals during metamorphism of manganese deposits. Typical associated minerals include hausmannite, galaxite, braunite, pyrolusite, coronadite, hematite and magnetite.
It was first described in 1869 and named for the Jakobsberg Mine, Nordmark, Filipstad, Värmland, Sweden.
...
Wikipedia