Bayldonite
Bayldonite (BAIL-done-ite) is a rare secondary mineral with the chemical formula PbCu3(AsO4)2(OH)2. It was first discovered in Penberthy Croft Mine, Cornwall, England, United Kingdom. It is named after its discoverer, John Bayldon (1837(8) – 1872). Specimens are also found in Tsumeb, Namibia, and Arizona, United States. It is sometimes used as a gemstone.
| Bayldonite | |
|---|---|
Bayldonite, Tsumeb, Namibia | |
| General | |
| Category | Arsenate minerals |
| Formula (repeating unit) | PbCu3(AsO4)2(OH)2 |
| IMA symbol | Bay |
| Strunz classification | 8.BH.45 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/c |
| Identification | |
| Color | Green, apple-green |
| Crystal habit | Mammillary crust |
| Twinning | Pseudoscalenohedral trillings with the composition plane |
| Cleavage | None observed |
| Fracture | Irregular/uneven, conchoidal, sub-conchoidal, fibrous |
| Tenacity | Brittle |
| Mohs scale hardness | 4+1⁄2 |
| Luster | Resinous, waxy, greasy |
| Streak | Siskin green to apple green |
| Diaphaneity | Transparent, translucent |
| Density | 5.24–5.65 g/cm3 (measured), 5.707 g/cm3 (calculated) |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.951 nβ = 1.970 nγ = 1.991 |
| Birefringence | 0.040 |
| Pleochroism | Non-pleochroic |
| 2V angle | 89° |
| Dispersion | r < v strong |
| Extinction | Y^elongation = 45°; X=b |
| References | |
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