Jacobsite

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<tr> <td>Chemical formula</td><td>iron(II,III) manganese oxide, MnFe₂O₄</td> </tr> <tr> <td>Color</td><td>Black</td> </tr><tr> <td>Crystal habit</td><td>Disseminated to massive</td> </tr><tr> <td>Crystal system</td><td>Isometric Hexoctahedral</td> </tr><tr> <td>Cleavage</td><td>none</td> </tr><tr> <td>Fracture</td><td>Conchoidal</td> </tr><tr> <td>Mohs Scale hardness</td><td>5.5 - 6.0</td> </tr><tr> <td>Luster</td><td>Metallic</td> </tr><tr> <td>Refractive index</td><td>Opaque</td> </tr><tr> <td>Streak</td><td>reddish black</td> </tr><tr> <td>Specific gravity</td><td>4.75</td> </tr>