xenotimeY

XenotimeY is a hypothetical mineral species within the xenotime phosphate group. It represents a solid-solution variant in which the Y-site is variably substituted by rare-earth elements, described by an idealized formula near (Y1−xREEx)PO4. The name reflects a yttrium-rich end member used in theoretical and experimental studies to examine how dopants affect the xenotime lattice and trace-element behavior.

Crystal chemistry and structure: Xenotime minerals, including xenotimeY in this concept, adopt a tetragonal lattice. Substituting Y by REE cations (such as Dy, Er, Yb, and others) would alter unit-cell dimensions and properties gradually with increasing x. The composition is modeled as a continuous solid solution rather than a fixed stoichiometry.

Occurrence and status: XenotimeY has not been confirmed in natural samples and is not listed in major mineral databases. It appears mainly in theoretical discussions and planned syntheses. If real, it would likely form in granitoid pegmatites and high-temperature hydrothermal veins where xenotime-group minerals are common.

Physical properties: As a xenotime analogue, xenotimeY would be expected to have a tetragonal habit, vitreous luster, and colors ranging from pale to brown. Typical related minerals show hardness around 6 and densities of roughly 4.3–4.9 g/cm3, with refractive indices near 1.82–1.90; exact values depend on substitution level x.

Research context and relevance: Studying xenotimeY would illuminate cation substitution in phosphate lattices and inform discussions of REE mobility in crustal environments. It would also provide a comparative framework for xenotime-(Y) and xenotime-(REE) systems.