Yttriaite-(Y): The natural occurrence of Y2O3 from the Bol'shaya Pol'ya River, Subpolar Urals, Russia

Abstract

Yttriaite-(Y), ideally Y_(2_O_(3), is a new mineral (IMA2010-039) from the alluvial deposits of the Bol’shaya Pol’ya River, Subpolar Urals, Russia. The new mineral occurs as isolated crystals, typically cubo-octahedra <6 µm in size, embedded in massive native tungsten. Associated minerals include: copper, zircon, osmium, gold, and pyrite. The main forms observed are {100} and {111}. Due to the crystal size, physical properties could not be determined; however, the properties of synthetic Y_(2)O_(3) are well known. Synthetic Y_(2)O_(3) crystals are colorless to white with a white streak; crystals are transparent with an adamantine luster, while massive Y2O3 is typically translucent with an earthy luster. Synthetic Y_(2)O_(3) has a Vickers hardness of 653.91, which corresponds to 5.5 on the Mohs scale. Synthetic Y_(2)O_(3) crystals have good cleavage on {111}. Yttriaite-(Y) is isotropic; the refractive index measured at 587 nm on synthetic Y_(2)O_(3) is n = 1.931. The empirical chemical formula (mean of 4 electron microprobe analyses) calculated on the basis of 3 O is: Y_(1.98)Dy_(0.01)Yb_(0.01O3). Yttriaite-(Y) is cubic, space group Ia3(overbar), with parameters a = 10.6018(7) A, V = 1191.62(7) A3, and Z = 16. The five strongest lines in the powder X-ray diffraction pattern (measured on synthetic Y_(2)O_(3) using synchrotron radiation) are [d_obs in A (I) (hkl)]: 3.0646 (100) (222), 1.8746 (55) (440), 1.5984 (38) (622), 2.6537 (26) (400), and 4.3356 (14) (211). The mineral name is based on the common name for the chemical compound, yttria.