Pyromorphite
| Pyromorphite | |
|---|---|
| General | |
| Category | Phosphate mineral Apatite group |
| Formula | Pb5(PO4)3Cl |
| IMA symbol | Pym |
| Strunz classification | 8.BN.05 |
| Crystal system | Hexagonal |
| Crystal class | Dipyramidal (6/m) (same H-M symbol) |
| Space group | P63/m |
| Identification | |
| Color | Dark green to grass-green or green, yellow, yellow-orange, reddish orange, yellow-brown, greenish-yellow or yellowish-green, shades of brown, tan, grayish, white and may be colorless; colourless or faintly tinted in transmitted light. |
| Crystal habit | Prismatic to acicular crystals, globular to reniform |
| Twinning | Rarely on {1122} |
| Cleavage | Imperfect- [1011] |
| Fracture | Uneven to sub-conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 3.5–4 |
| Luster | Resinous to subadamantine |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 7.04 measured, 7.14 calculated |
| Optical properties | Uniaxial (−) May be anomalously biaxial (−) |
| Refractive index | nω = 2.058 nε = 2.048 |
| Birefringence | δ = 0.010 |
| Pleochroism | Weak |
| Ultraviolet fluorescence | May fluoresce yellow to orange under LW and SW UV |
| Other characteristics | Piezoelectric if biaxial |
| References | |
Pyromorphite is a mineral species composed of lead chlorophosphate: Pb5(PO4)3Cl, sometimes occurring in sufficient abundance to be mined as an ore of lead. Crystals are common, and have the form of a hexagonal prism terminated by the basal planes, sometimes combined with narrow faces of a hexagonal pyramid. Crystals with a barrel-like curvature are not uncommon. Globular and reniform masses are also found.
Pyromorphite is part of the apatite group of minerals and bears a close resemblance physically and chemically with two other minerals: mimetite (Pb5(AsO4)3Cl) and vanadinite (Pb5(VO4)3Cl). The resemblance in external characters is so close that, as a rule, it is only possible to distinguish between them by chemical tests. They were formerly confused under the names green lead ore and brown lead ore (German: Grünbleierz and Braunbleierz).