Physical Properties |
|
| Chemical formula | FeO(OH) |
| Class | Hydroxide |
| Crystal system | Orthorhombic |
| Habit | Platy Prismatic Fibrous Botryoidal Mammillary |
| Color | Yellow-brown Dark brown Black |
| Hardness | 5 to 5.5 |
| Specific gravity | 4.3 |
| Cleavage | Perfect (010) (rare) |
| Fracture | Uneven |
| Luster | Subadamantine to earthy |
| Transparency | Subtranslucent to opaque |
| Streak | Brown-yellow |
Optical Properties |
|
| PPL | Yellow Orange-red Various browns Pleochroic High relief |
| XPL | 4th order interference colors; may be masked by mineral color |
| δ | 0.15 |
| after Perkins, 379-380 |
Goethite in Hand Sample
Geothite in Thin Section
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