Grayite
Grayite, ThPO4·(H2O), is a thorium phosphate mineral of the Rabdophane group first discovered in 1957 by S.H.U. Bowie in Rhodesia. It is of moderate hardness occurring occasionally in aggregates of hexagonal crystals occasionally but more commonly in microgranular/cryptocrystalline masses. Due to its thorium content, grayite displays some radioactivity although it is only moderate and the mineral displays powder XRD peaks without any metamict-like effects. The color of grayite is most commonly observed as a light to dark reddish brown but has also been observed as lighter yellows with grayish tints. It has a low to moderate hardness with a Mohs hardness of 3–4 and has a specific gravity of 3.7–4.3. It has been found in both intrusive igneous and sedimentary environments.
| Grayite | |
|---|---|
| General | |
| Category | Phosphate minerals Rhabdophane group |
| Formula (repeating unit) | (Th,Pb,Ca)PO4·(H2O) |
| IMA symbol | Gry |
| Strunz classification | 8.C.J.45 |
| Dana classification | 40.04.07.04 |
| Crystal system | Hexagonal |
| Crystal class | Trapezohedral (622) (same H-M symbol) |
| Space group | P6222 or P6422 |
| Unit cell | a = 6.957 c = 6.396 [Å]; Z = 3 |
| Identification | |
| Color | Pale yellow, yellow, yellowish gray, often a dark reddish brown |
| Crystal habit | Cryptocrystalline Aggregate |
| Mohs scale hardness | 3–4 |
| Luster | Resinous to waxy to greasy |
| Diaphaneity | Semitransparent |
| Density | 6.41 g/cm3 (calculated) |
| Optical properties | Uniaxial |
| Refractive index | nα = 1.66 nβ = 1.69 |
| Birefringence | Moderate with max at δ = 1.660 |
| Ultraviolet fluorescence | May fluoresce green or yellow under short wave UV |
| Other characteristics | Radioactive |
| References | |