Stolzite
Stolzite is a very rare sulfate mineral and an extremely rare gem. It is a very heavy mineral with a density of about 8.0 (g/cm3) and has a very high refractive index of 2.19 – 2.27 and an adamantine to resinous luster but is very soft with a Mohs hardness of 2.5 – 3.0. Stolzite is found at many localities in small amounts but very few localities produce crystals large enough for faceting. The few locations that might produce gem quality crystals are the Sainte-Lucie mine, Saint-Léger de Peyre, Lozére, France; fine examples from Broken Hill, New South Wales, Australia; large crystals from Tsumeb, Namibia. In the USA, large crystals at the Fat Jack mine, Bradshaw Mountains, Yavapai County, Arizona.
| Category: | Tungstate minerals |
| Formula: | PbWO4 |
| lead tungstate | |
| Crystallography: | Tetragonal – Dipyramidal |
| Crystal Habit: | Crystals are commonly dipyramidal {111}, {101}, with {011}, {112}, {001}, complex development with over 30 other forms recorded; may be flat tabular {001}, {101}, to 6 cm. |
| Twinning: | None |
| Cleavage: | [001] Indistinct, [011] Imperfect |
| Fracture: | Irregular/Uneven, Conchoidal |
| Tenacity: | Brittle |
| Hardness (Mohs): | 2.5 – 3.0 |
| Density: | 7.90 – 8.34 (g/cm3) |
| Luminescence: | May be bright red to red-orange (LW UV), and lemon-yellow (SW UV). |
| Radioactivity: | Not Radioactive |
| Other: | Melting Point 1123° C |
| Color: | Reddish brown, Brown, Yellowish Gray, Smoky Gray, Straw-Yellow, Lemon-Yellow; may be Green, Orange, Red |
| Transparency: | Transparent to Translucent |
| Luster: | Sub-Adamantine, Resinous |
| Refractive Index: | 2.19 – 2.27 Uniaxial ( – ) |
| Birefringence: | 0.080 – 0.090 |
| Pleochroism: | None |
