| Jacobsite | |
| Category: | Oxide minerals Spinel group Spinel structural group |
| Formula: | iron(II,III) manganese oxide, (Mn,Mg)Fe2O4 |
| Imasymbol: | Jcb[1] |
| Strunz: | 4.BB.05 |
| System: | Isometric |
| Class: | Hexoctahedral (mm) H-M symbol: (4/m 2/m) |
| Symmetry: | Fdm (no. 227) |
| Unit Cell: | a = 8.457 Ă…; Z = 8 |
| Color: | Black to brownish black |
| Habit: | Disseminated to massive, rarely as octahedral crystals |
| Twinning: | Spinel law, flattened on or lamellar |
| Cleavage: | , probably a parting |
| Fracture: | Conchoidal |
| Mohs: | 5.5–6.5 |
| Luster: | Metallic |
| Refractive: | ~2.3 |
| Opticalprop: | Isotropic |
| Streak: | reddish black to brown |
| Gravity: | 4.76 |
| Diaphaneity: | Opaque |
| Other: | 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]
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]
