Xenotime
Xenotime is a rare-earth phosphate mineral, the major component of which is yttrium orthophosphate (YPO4). It forms a solid solution series with chernovite-(Y) (YAsO4) and therefore may contain trace impurities of arsenic, as well as silicon dioxide and calcium. The rare-earth elements dysprosium, erbium, terbium and ytterbium, as well as metal elements such as thorium and uranium (all replacing yttrium) are the expressive secondary components of xenotime. Due to uranium and thorium impurities, some xenotime specimens may be weakly to strongly radioactive. Lithiophyllite, monazite and purpurite are sometimes grouped with xenotime in the informal "anhydrous phosphates" group. Xenotime is used chiefly as a source of yttrium and heavy lanthanide metals (dysprosium, ytterbium, erbium and gadolinium). Occasionally, gemstones are also cut from the finest xenotime crystals.
| Xenotime | |
|---|---|
Xenotime with rutile | |
| General | |
| Category | Phosphate minerals |
| Formula (repeating unit) | YPO4 |
| IMA symbol | Xtm |
| Strunz classification | 8.AD.35 |
| Crystal system | Tetragonal |
| Crystal class | Dipyramidal (4/mmm) H-M symbol: (4/m) |
| Space group | I41/a |
| Identification | |
| Color | Brown, brownish yellow, gray |
| Crystal habit | Prismatic, radial aggregates, granular |
| Cleavage | Perfect [100] |
| Fracture | Uneven to splintery |
| Mohs scale hardness | 4.5 |
| Luster | Vitreous to resinous |
| Streak | Pale brown, yellowish or reddish, to white |
| Diaphaneity | Translucent to opaque |
| Specific gravity | 4.4–5.1 |
| Refractive index | 1.720–1.815 |
| Birefringence | δ = 0.096 |
| Pleochroism | Dichroic |
| Other characteristics | Not radioactive or luminescent |
| References | |