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| Bayldonite | |
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| Category: | Arsenate minerals |
| Formula: | PbCu3(AsO4)2(OH)2 |
| Imasymbol: | Bay[1] |
| Strunz: | 8.BH.45 |
| System: | Monoclinic |
| Class: | Prismatic (2/m) (same H-M symbol) |
| Symmetry: | C2/c |
| Color: | Green, apple-green |
| Habit: | Mammillary crust |
| Twinning: | Pseudoscalenohedral trillings with the composition plane |
| Cleavage: | None observed |
| Fracture: | Irregular/uneven, conchoidal, sub-conchoidal, fibrous |
| Tenacity: | Brittle |
| 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) |
| Opticalprop: | Biaxial (+) |
| Refractive: | nα = 1.951 nβ = 1.970 nγ = 1.991 |
| Birefringence: | 0.040 |
| Pleochroism: | Non-pleochroic |
| 2V: | 89° |
| Dispersion: | r < v strong |
| Extinction: | Y^elongation = 45°; X=b |
| References: | [2] [3] [4] |
Bayldonite (BAIL-done-ite) is a rare secondary mineral with the chemical formula PbCu3(AsO4)2(OH)2. Its provenance has been attributed to Penberthy Croft Mine, Cornwall, England, United Kingdom but there is no substantiating evidence for this and it was only attributed to Cornwall by Church (1865). Also, Church’s paper (Church, 1865) clearly states “I am indebted to Mr. Talling for this mineral species also.” so the original material was supplied by the mineral dealer Richard Talling and not discovered by Bayldon. [5] [6] Bayldonite was named after Church's dear friend and colleague at the Royal Agricultural College (RAC),Cirencester, Gloucestershire John Bayldon MD (1837 – 1872).[7] Specimens are also found in Tsumeb, Namibia, and Arizona, United States. It is sometimes used as a gemstone.[8]