Bayldonite (BAIL-done-ite)[5] 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.[5] It is named after its discoverer, John Bayldon (1837(8) – 1872).[6] Specimens are also found in Tsumeb, Namibia, and Arizona, United States. It is sometimes used as a gemstone.[7]
Bayldonite | |
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General | |
Category | Arsenate minerals |
Formula (repeating unit) | PbCu3(AsO4)2(OH)2 |
IMA symbol | Bay[1] |
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 | [2][3][4] |