Pyromorphite
Pyromorphite is a fairly common mineral but very rarely faceted. Its molecular weight is 1,356.37 gm. It is a secondary lead mineral found in the oxidized zones of lead deposits. Typically found as green to yellow barrel-shaped hexagonal prisms, in clusters or as druses on matrix. Pyromorphite has a specific gravity of 7.04 (g/cm3) and the refractive index of 2.049 – 2.059 Uniaxial ( – ); may be anomalously Biaxial ( – ), sectored. Pyromorphite has the same structure as Apatite so crystals of the two will have similar shapes. Pyromorphite also forms a chemical series with Mimetite (Pb5(AsO4)3Cl) and Vanadinite (Pb5(VO4)3Cl). It can be very difficult to tell the difference between green Mimetite or yellow Pyromorphite, but usually Pyromorphite is green and Mimetite is yellow. Vanadinite is usually red.
The main sources of large, bright green, gemmy crystals are Guilin Prefecture, Guangxi Zhuang Autonomous Region, China; Ussel, Corrèze, Limousin, France, Villaviciosa de Córdoba, Sierra Morena, Córdoba, Andalusia, Spain; and Coeur d’Alene District, Shoshone County, Idaho, USA.
| Category: | Phosphate mineral Apatite group |
| Chemical Formula: | Pb5(PO4)3Cl |
| Molecular Weight: | 1,356.37 gm |
| Crystallography: | Hexagonal – Dipyramidal |
| Crystal Habit: | Crystals short to long prismatic, may be acicular [0001], with prominent [1010], [0001], [1011], [2021], hoppered terminations typical, to 8 cm, rarely tabular to equant; radiating to branching groups, tapering to a point. Commonly rounded, globular, reniform, botryoidal. |
| Twinning: | On [1122], very rare |
| Cleavage: | [1011] Imperfect |
| Fracture: | Irregular, Uneven, Subconchoidal |
| Tenacity: | Brittle |
| Hardness (Mohs): | 3.5 – 4.0 |
| Density: | 7.04 (g/cm3) |
| Luminescence: | None or may fluoresce yellow to orange under LW and SW UV. |
| Radioactivity: | Not Radioacitve |
| Other: | Piezoelectric if Biaxial (may be anomalously Biaxial) |
| Color: | Green, Yellow, Brown, Grayish White, Yellowish Red |
| Transparency: | Transparent to Translucent |
| Luster: | Adamantine, Resinous |
| Refractive Index: | 2.049 – 2.059 Uniaxial ( – ); may be anomalously Biaxial ( – ), sectored |
| Birefringence: | 0.0100 (very high) |
| Dispersion: | Very Strong; r > v |
| Pleochroism: | Weak |
