Springcreekite, BaV33+(PO4)(2)(OH,H2O)(6), a new member of the crandallitegroup, from the Spring Creek mine, South Australia: the first natural V3+-member of the alunite family and its crystal structure

Springcreekite, ideally BaV33+(PO4)(2)(OH,H2O)(6), is a new member of the c randallite group and the first naturally occurring V3+-member of the alunit e family. Springcreekite occurs as an extremely rare mineral on the dumps o f the Spring Creek copper mine near Wilmington, southern Flinders Ranges, S outh Australia. It forms very small (less than or equal to 0.1 mm), pseudoc ubic rhombohedra {10 (1) over bar 2}, and is associated with quartz, copper , cuprite, goethite, whitlockite, mitridatite and the new species bariosinc osite. Springcreekite is black, with a brownish black streak and adamantine to semimetallic lustre. It is brittle, has a parting or poor cleavage para llel to {10 (1) over bar 2}, an irregular fracture, a Mohs hardness of simi lar to 4-5, and D(meas.) 3.48(3), D(calc.) 3.58 g/cm(3). Optically, it is u niaxial negative, with omega = 1.858 +/- 0.005, epsilon = 1.817 +/- 0.004. Pleochroism is very strong, E pale brownish to brownish, O blackish brown t o black, and absorption O > E. Electron microprobe analysis yielded (wt.%): BaO 23.34, SrO 0.27, CaO 0.15, Na2O 0.08, V2O3 19.44, Fe2O3 15.02, Al2O3 0 .32, CuO 0.17, ZnO 0.14, P2O5 23.26, SiO2 0.20, F 0.21, H2O 12.16 (calc.), less O=F -0.09, sum 94.67, giving the empirical formula (Ba0.92Ca0.02Sr0.02 Na0.02)(Sigma 0.98)-(V1.573+Fe3+ 1.14Al0.05Cu0.01Zn0.01)(Sigma 2.78) [(P0.9 9Si0.01) O-4)](2)(OH4.17F0.07H2O1.76)(Sigma 6.00), based on two (P + Si). A V3+-richer co-type specimen has the formula (Ba0.94Sr0.04Na0.01)(Sigma 0.9 9)(V2.093+Fe0.613+Al0.06Cu0.04)(Sigma 2.80)(PO4)(2)(OH4.41F0.02H2O1.57)(Sig ma 6.00) Springcreekite is rhombohedral, space group R (3) over bar m, with a 7.258(1), c 17.361(9) Angstrom, V 792.0(4) Angstrom(3), and Z = 3. Stron gest lines in the X-ray powder diffraction pattern are: [d in Angstrom (I) hkl] 3.073 (10) 113, 5.90 (9) 101, 1.971 (5) 303, 3.627 (4) 110, 2.301 (4) 107, 122, 1.814 (4) 220. A single-crystal structure refinement (R = 2.9 %; data collected with a CCD detector) confirmed the crandallite-type structur e of springcreekite. The atomic arrangement consists of (V3+,Fe3+)O-6 octah edra, PO4 tetrahedra and Ba in 12-fold coordination. Springcreekite is name d after the locality. The type and co-type specimens are deposited at the S outh Australian Museum, Adelaide, Australia.