Liguowuite, WO3, a new member of the A-site vacant perovskite type minerals from the Panzhihua–Xichang region, China

A new member of the non-stoichiometric perovskite group mineral species, liguowuite, ideally WO3, has been found in the Neoproterozoic Sinian biotite-quartz monzonite in the southern part of the Panzhihua–Xichang region (Nanyang village: 26∘46′8.21′′ N, 101∘27′13.86′′ E), China. It is associated with hornblende, pargasite, ferro-hornblende, annite, hydrobiotite, phlogopite, orthoclase, microcline, albite, quartz, kaolinite, ilmenite, goethite, hematite, magnetite, pyrite, zircon, zoisite, titanite, epidote, diopside, tourmaline, almandine, fluorapatite, monazite-(Ce), allanite-(Ce), bastnäsite-(Ce), xenotime-(Y), scheelite, moissanite, tellurite, wumuite, and tewite. Liguowuite occurs as greenish yellow prisms, ranging from 0.05 to 0.1 mm in diameter, and it is transparent with a greasy luster and a white streak. Liguowuite exhibits a triclinic pseudomorphism composed of nanoparticles with many cracks and nanovoids. This mineral is brittle and has a Mohs hardness value of approximately 3–4. The calculated density is 7.22 g cm-3. Electron microprobe analyses gave (average weight percent, wt %, of 15 spot analyses of 4 samples) K2O = 0.01, WO3 = 99.23, TeO2 = 0.03, CaO = 0.06, Na2O = 0.04, and total 99.37, yielding the empirical formula W1.00O3, based on Oapfu=3 and ideallyWO3. The strongest five diffraction lines (d Å (I)(hkl)) are 3.8552 (88)(002), 3.7685 (88)(020), 3.6590 (100)(–200), 2.6928 (43)(022), and 2.6258 (60)(202). Liguowuite is monoclinic and is in space groupP21/n, with a= 7.32582(18) Å, b= 7.54767(18) Å, c= 7.71128(18) Å, β= 90.678(3)∘, V= 426.348(19) Å3, and Z= 8. The crystal structure data were refined using the Rietveld refinement method and X-ray powder diffraction data. The reliability factors (R factors) were Rwp= 0.0604 and Rp= 0.0454, with χ2 = 1.707. Liguowuite consists of corner-sharing distorted and tilted [WO6] octahedra, in which the W atoms are off-center and form six W–O bonds ranging from 1.7 to 2.2 Å with the surrounding oxygen atoms. According to the hierarchical scheme for perovskite supergroup minerals, liguowuite is the first reported example ofA-site vacant single oxide, i.e., a new perovskite subgroup.