Abstract

Wernerbaurite, {[Ca(H2O)7]2(H2O)2(H3O)2}{V10O28}, and schindlerite, {[Na2(H2O)10](H3O)4}{V10O28}, are new mineral species from the St. Jude mine, Slick Rock district, San Miguel County, Colorado, U.S.A. Crystals of wernerbaurite are tabular on {100} with stepped faces and square to octagonal outlines, up to about 1 mm in maximum dimension; the crystals are yellow-orange and the streak is yellow. The mineral displays a subadamantine luster, and is transparent; it does not fluoresce in short- or long-wave ultraviolet radiation. Wernerbaurite has a hardness of about 2, a brittle tenacity, and irregular fracture; two good cleavages, {100} and {010}, were observed. The density calculated from the empirical formula using the single-crystal cell data is 2.352 g cm−3. Wernerbaurite is biaxial (−), with α 1.745(3), β 1.780(3), and γ 1.795(3); 2V 66(2)° (white light). Dispersion is r > v, very strong. Optical orientation: X ^ a = 29°, Y ^ c = 44°, Z ^ b = 46°; pleochroism: X, Z = yellow, Y = orange; X = Z < Y. Electron probe microanalysis and the crystal structure solution provided the empirical formula {(Ca1.88Na0.14K0.03Sr0.02) ∑2.07(H2O)15.95(H3O)2.05}{V10O28} (based on V5+ = 10 and O = 46). The simplified structural formula of wernerbaurite is {[Ca(H2O)7]2(H2O)2(H3O)2}{V10O28}. Wernerbaurite is triclinic, P1̅, with a 9.7212(6), b 10.2598(8), c 10.5928(8) Å, α 89.999(6)°, β 77.083(7)°, γ 69.887(8)°, V 963.55(12) Å3, and Z = 1. The strongest four lines in the diffraction pattern [d in Å(I)(hkl)] are: 10.32(100)(001), 8.88(95)(100), 9.64(92)(010), and 6.881(70)(111). The atomic arrangement of wernerbaurite was refined to R1 = 0.0341 on the basis of 3,440 diffractions with Fo > 4σF. The structural unit is a decavanadate polyanion, (V10O28)6−. The interstitial unit linking the structural units has a composition of {[Ca(H2O)7]2(H2O)2(H3O)2}6+, and is formed of an isolated [Ca(H2O)7]2+ polyhedron, a (H3O)+ ion, and an isolated H2O molecule. Wernerbaurite is named in honor of Prof. Dr. rer. nat. Werner H. Baur for his long, productive and distinguished career in mineralogical crystallography.

Crystals of schindlerite are tabular and commonly occur in stacked parallel intergrowths up to 0.3 mm in maximum dimension; the crystals are orange with a yellow streak. Schindlerite displays a subadamantine luster, and is transparent; it does not fluoresce in short- or long-wave ultraviolet radiation. Schindlerite has a hardness of about 2, a brittle tenacity, and one good cleavage on {010}. The density calculated from the empirical formula using the single-crystal cell data is 2.461 g cm−3. Schindlerite is biaxial (+), with α 1.74 (est), β 1.790(5), and γ 1.875 (calc); 2V (meas) = 78.1° (white light). Dispersion is r > v, very strong. The optical orientation is X ^ b = 25°, Y ^ c = 12°, Z ^ a = 3°. No pleochroism was perceptible. Electron probe microanalysis and the crystal structure solution provided the empirical formula {[(Na1.58K0.35Ca0.02Sr0.01)1.96(H2O)10.00] (H3O)4}{V10O28} (based on V5+ = 10 and O = 42 ). The simplified structural formula of schindlerite is {[Na2(H2O)10](H3O)4}{V10O28}. Schindlerite is triclinic, P1̅, with a 8.5143(3), b 10.4283(5), c 11.2827(8) Å, α 68.595(5)°, β 87.253(6)°, γ 67.112(5)°, V 854.08(8) Å3, and Z = 1. The strongest four lines in the diffraction pattern [d in Å(I)(hkl)] are: 8.68(100)(010, 011), 10.51(94)(001), 7.70(86)(100,110), and 6.73(61)(111,1̅01). The atomic arrangement of schindlerite was refined to R1 = 0.0399. The structural unit is a decavanadate polyanion, (V10O28)6−. The interstitial unit linking the structural units has a composition of {[Na2(H2O)10](H3O)4}6+, and is formed of a [Na2(H2O)10] dimer decorated with four hydronium ions. As in wernerbaurite, an extensive network of hydrogen bonding links the interstitial unit to the structural unit in schindlerite. Schindlerite is named in honor of Dr. Michael Schindler, Associate Professor for Environmental Mineralogy at Laurentian University, Sudbury, Ontario, who has contributed greatly to our understanding of vanadium mineralogy. Wernerbaurite and schindlerite are the first hydronium-bearing decavanadate minerals, and both minerals are natural analogs of previously described synthetic phases.

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