Xenotime - YPO4
Xenotime is a rare earth phosphate mineral (YPO4). Due to uranium and thorium impurities, some xenotime specimens may be weakly to strongly radioactive. The etymology of the name xenotime is from the Greek words vain and honor because the yttrium contained within it was first thought to be a new element. Xenotime was first described for an occurrence in Vest-Agder, Norway in 1832. The structure of xenotime is analogous to Zircon ZrSiO4, with PO4- tetrahedral units replacing SiO4-. Other rare earth elements, especially erbium may partially replace Y. Zr, Th, U or Ca may also replace some Y; the PO4- tetrahedral units can be replaced by SO24- ore by SiO4-. Xenotime is a very rare mineral, it is an accessory mineral in some alkaline granite, syenite and similar siliceous rocks.Optical properties:
• Color: Colorless or pale yellow-brown
• Form: Euhedral stubby bipyramidal crystals
• Relief: Moderate
• Interference colors: Very strong
Bibliography
• Cox et al. (1979): The Interpretation of Igneous Rocks, George Allen and Unwin, London.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Le Maitre, R. W., Streckeisen, A., Zanettin, B., Le Bas, M. J., Bonin, B., Bateman, P., & Lameyre, J. (2002). Igneous rocks. A classification and glossary of terms, 2. Cambridge University Press.
• Middlemost, E. A. (1986). Magmas and magmatic rocks: an introduction to igneous petrology.
• Shelley, D. (1993). Igneous and metamorphic rocks under the microscope: classification, textures, microstructures and mineral preferred-orientations.
• Vernon, R. H. & Clarke, G. L. (2008): Principles of Metamorphic Petrology. Cambridge University Press.
.jpg) Xenotime (high relief) and arfvedsonite crystals (blue). PPL image, 10x (Field of view = 2mm) |
.jpg) Xenotime (high relief) and arfvedsonite crystals (blue). PPL image, 10x (Field of view = 2mm) |
.jpg) Xenotime (high interference colors) crystals in a fine-grained matrix made of quartz and feldspar (I order gray). Brandberg Complex (Namibia). XPL image, 10x (Field of view = 2mm) |
.jpg) Xenotime (high interference colors) crystals in a fine-grained matrix made of quartz and feldspar (I order gray). Brandberg Complex (Namibia). XPL image, 10x (Field of view = 2mm) |
.jpg) Aegirine (grass-green) crystals and xenotime crystals (high relief). Brandberg Complex (Namibia). PPL image, 2x (Field of view = 7mm) |
.jpg) Xenotime (high relief) and arfvedsonite crystals (blue). PPL image, 10x (Field of view = 2mm) |