- The composition, lattice parameters, and elastic constants of natural single crystal YPO4 xenotime from Novo Horizonte (Brazil) were determined using EPMA, XRD, and the pulse-echo technique. The composition indicates a 24% substitution of Y sites with other rare-earth elements. The lattice parameters of the studied crystal deviated only slightly from those reported for synthetic YPO4 and were in a good agreement with trends obeyed by other orthophosphates with the xenotime structure. The measured elastic constants C 11, C 33, C 44, and C 66 were consistent with synthetic crystals when porosity was accounted for. C 12 and C 13 constants were evaluated based on the comparison with other materials with xenotime structure. The elastic constants could be rationalized using interionic force constants and bond energies.