Johnbaumite
Johnbaumite is a calcium arsenate hydroxide mineral. It was first described in 1980, where it appeared in Franklin Township, Somerset County, New Jersey. Johnbaumite was discovered at Harstigen mine in Sweden in the 19th century, but it was described as svabite.
| Johnbaumite | |
|---|---|
| General | |
| Category | Apatite group |
| Formula (repeating unit) | Ca5(AsO4)3OH |
| IMA symbol | Jbm |
| Strunz classification | 08.BN.05 |
| Dana classification | 41.08.03.03 |
| Crystal system | Hexagonal |
| Crystal class | Dipyramidal (8/m) |
| Space group | P63/m |
| Identification | |
| Colour | Greyish white to colourless |
| Crystal habit | Anhedral grains, granular minerals without the expression of crystal shapes and massive, uniformly indistinguishable crystals forming large masses. |
| Cleavage | Distinct {1010} |
| Fracture | Irregular/Uneven |
| Tenacity | Brittle |
| Mohs scale hardness | ≈ 4.5 |
| Luster | Adamantine to greasy on fracture surfaces, vitreous on cleavage surfaces |
| Streak | White |
| Diaphaneity | Transparent |
| Density | 3.65 – 3.73 g/cm3 |
| Optical properties | Uniaxial (−) |
| Refractive index | nω = 1.687 nε = 1.684 |
| Birefringence | 0.003 |
| Pleochroism | Non-pleochroic |
| Extinction | Parallel |
| References | |
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