Mansfieldite
Mansfieldite is a very rare phosphare mineral that is usually found as opaque to semi-transparent crusts or in massive form. It is extremely rare to find pseudo-octahedral crystals and these are very small, to 2 mm. Its coloring is typically white to pale gray, light green to bluish green and rarely shades of pink when cobalt bearing.
There are very few localities for finding Mansfieldite. Some of these are Djebel Debar, northeast of Hammam Meskhoutine, Qacentina (Constantine), Algeria; on Mt. Cobalt, 110 km south of Cloncurry, Queensland, Australia; and in the Bota-Burum uranium deposit, 15 km southwest of Alakol Lake, Chu-Ili Mountains, southwestern Balkhash district, Kazakhstan.
| Formula: | AlAsO4 · 2H2O |
| Crystallography: | Orthorhombic – Dipyramidal |
| Crystal Habit: | Rarely in pseudo-octahedral crystals, to 2 mm; commonly as crusts, and porous to cellular masses with spherulitic structure. |
| Twinning: | None |
| Cleavage: | [201] Imperfect/Fair, [001] Imperfect |
| Fracture: | Sub-Conchoidal |
| Tenacity: | Brittle |
| Hardness (Mohs): | 3.5 – 4.0 |
| Density: | 3.03 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Health Warning: | CAUTION: Contains Arsenic, a poisonous element – always wash hands after handling. Avoid inhaling dust when handling or breaking. Never lick or ingest. |
| Color: | White to pale Gray, light Green to Bluish Green |
| Transparency: | Opaque to Semi-Transparent |
| Luster: | Vitreous |
| Refractive Index: | 1.622 – 1.663 Biaxial ( + ) |
| Birefringence: | 0.0200 – 0.0320 |
| Dispersion: | Strong; r > v |
| Pleochroism: | None |
