Johnbaumite
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| Johnbaumite | |
|---|---|
 | |
| General | |
| Category | Apatite group |
| Formula | Ca5(AsO4)3OH |
| IMA symbol | Jbm[1] |
| 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 | [2][3] |
Johnbaumite is a calcium arsenate hydroxide mineral. It was first described in 1980, where it appeared in Franklin, Sussex County, New Jersey.[4] Johnbaumite was discovered at Harstigen mine in Sweden in the 19th century, but it was described as svabite.[5]
It is named after geologist John Leach Baum (March 15, 1916 – October 16, 2011), who found the original specimen in 1944. He was a significant contributor to the geology and mineralogy of the Franklin deposit, and the Curator Emeritus at the Franklin Mineral Museum.