Drysdallite is a rare molybdenum selenium sulfide mineral with formula Mo(Se,S)2. It crystallizes in the hexagonal system as small pyramidal crystals or in cleavable masses. It is an opaque metallic mineral with a Mohs hardness of 1 to 1.5 and a specific gravity of 6.25. Like molybdenite it is pliable with perfect cleavage.
| Drysdallite | |
|---|---|
 | |
| General | |
| Category | Mineral |
| Formula (repeating unit) | MoSe1.5S0.5 |
| IMA symbol | Dry[1] |
| Strunz classification | 2/D.25-30 |
| Dana classification | 1.12.10.2 |
| Crystal system | Hexagonal - Dihexagonal Dipyramidal |
| Space group | P63/mmc (No. 194) |
| Unit cell | 120.94 ų (Calculated from Unit Cell) |
| Identification | |
| Formula mass | 230.41 gm |
| Colour | Grayish-black |
| Cleavage | Perfect |
| Tenacity | Waxy, pliable, difficult to pulverise |
| Mohs scale hardness | 2 |
| Luster | Metallic |
| Streak | Brown-black |
| Specific gravity | 6.248 (Calculated) |
| Density | 6.248 g/cm3 (Calculated) |
| Pleochroism | Strong, white to very pale grey, to pinkish grey |
It was first described in 1973 for an occurrence in an oxidized uranium deposit near Solwezi, Zambia. It was named for Alan Roy Drysdall, the director of the Zambian geological survey.