Wumuite (KAl 0.33W 2.67O 9) – a new mineral with an HTB-type structure from the Panzhihua–Xichang region in China

Xue, Yuan; Li, Guowu; Xie, Yingmei

Wumuite, ideally inline-formulaKAl0.33W2.67O9, is a new mineral species found in the Neoproterozoic Sinian light-weathered biotite–quartz monzonite in the southern part of the Panzhihua–Xichang region (Nanyang village: 26inline-formula46inline-formula8.21inline-formula′′ N, 101inline-formula27inline-formula13.86inline-formula′′ E), China. It is associated with quartz, orthoclase, albite, biotite, hornblende, kaolinite, ilmenite, goethite, hematite, zircon, zoisite, tourmaline, monazite-(Ce), allanite-(Ce), scheelite, tellurite, tewite, and an unidentified, potentially new mineral corresponding to inline-formulaWO3. Wumuite occurs as light green hexagonal tabular crystals, is up to 0.3 mm in diameter, and has a vitreous to adamantine luster and a white streak; i.e., it is transparent. The mineral is brittle with good cleavage parallel to inline-formula M10inlinescrollmathml italic { normal 10 true normal 1 normal ¯ normal 0 italic } 38pt14ptsvg-formulamathimg8df949e7ba275a3ebabc9825b76cabbb ejm-32-483-2020-ie00001.svg38pt14ptejm-32-483-2020-ie00001.png and inline-formula{0001}. It has a Mohs hardness of about 5–6 and a calculated density of 6.52 inline-formulag cm−3. Electron microprobe analyses yielded the following (in wt % – average of 10 spot analyses of one sample): inline-formulaK2O 5.55, inline-formulaWO3 91.16, inline-formulaTeO2 0.59, and inline-formulaAl2O3 2.52, with a total of 99.82. The empirical formula for wumuite calculated on the basis of inline-formulaOapfu=9 is inline-formulaK0.80(W2.68Al0.34Te0.03)∑3.05O9, ideally inline-formulaK(W2.67Al0.33)∑3O9 or inline-formulaKAl0.33W2.67O9. The strongest four diffraction lines [inline-formulad Å (inline-formulaI) (hkl)] are 6.261(36)(010), 3.727(30)(001), 3.161(100)(020), and 2.413(40)(021). Wumuite is hexagonal, in space group inline-formulaP6/mmm, with inline-formulaa=7.2952(5) Å, inline-formulac=3.7711(3) Å, inline-formulaV=173.81(2) Åinline-formula3, and inline-formulaZ=1. The crystal structure was solved and refined to a reliability factor of inline-formulaR1[inline-formula M30inlinescrollmathml F normal 2 > normal 4 italic σ ( F normal 2 ) ] = normal 0.025 104pt15ptsvg-formulamathimgd5b4922c97500b973285c5cf232c1ced ejm-32-483-2020-ie00002.svg104pt15ptejm-32-483-2020-ie00002.png (wRinline-formula2=0.072) based on 164 unique reflections (777 measured reflections, inline-formulaR(int)=0.011). Wumuite has a hexagonal tungsten bronze (HTB)-type structure. The layers of corner-sharing inline-formula[(W,Al)O]6 octahedra, with the layers oriented normal to the short (3.7713 Å) inline-formulac repeat and along with the W–O–W links, connect to form a hexagonal ring channel (tunnel). K is distributed in the hexagonal channel. An associated new mineral, tewite, which was discovered in the same area, also has a new tungsten bronze (TB)-type-related structure and has a genetic connection with wumuite in both back-scattered electron (BSE) images and synthetic experiments. The formation of wumuite is likely related to the nearby quartz-vein-type Au mineralization. The mineral was formed by a metasomatic reaction between W-rich hydrothermal fluids and the potassium feldspar in the monzonite.

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Xue, Yuan / Li, Guowu / Xie, Yingmei: Wumuite (KAl0.33W2.67O9) – a new mineral with an HTB-type structure from the Panzhihua–Xichang region in China. 2020. Copernicus Publications.

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