WEINEBENEITE, CABE3(PO4)2(OH)2.4H2O, A NEW MINERAL SPECIES - MINERAL DATA AND CRYSTAL-STRUCTURE

Weinebeneite is a new mineral species from a spodumene pegmatite at Weinebene that occurs in the high-grade metamorphic rocks of Koralpe, Carinthia, Austria. It occurs in small fractures as a secondary mineral associated with fairfieldite, roscherite and uralolite. It forms clear, colorless, vitreous, platy crystals up to 0.1 x 0.3 x 0.5 mm surrounding rosettes of xenomorphic weinebeneite up to 20 mm in diameter. It is brittle with a splintery fracture. Mohs' hardness is 3 - 4; d(meas.) = 2.15(4) g/cm3 and d(calc.), = 2.17 g/cm3. Optically, weinebeneite is biaxial positive but nearly uniaxial with 2V(gamma)meas. < 10-degrees ; n(alpha) = 1.520, n(beta) = 1.520, n(gamma) = 1.530 (589 nm); Z : c = 42-degrees in acute angle beta. Weinebeneite is monoclinic, a = 11.897(2), b = 9.707(1), c = 9.633(1) angstrom, b = 95.76(1)-degrees, V = 1106.8(3) angstrom3 and z = 4. The three strongest lines of the X-ray powder diffraction pattern are [d (angstrom), (hkl), I] : 2.513, (223BAR), 100 ; 3.421, (221), 70 ; 5.92, (200), 60. The combined results of electron-microprobe, atomic absorption, electron energy-loss-spectroscopy analyses and structure refinement yield the formula Ca0.99Be3.02P1.97 07.88(OH)2.11.4H2O ( based on O = 14) or, ideally, CaBe3(PO4)2(OH)2.4H2O. The name refers to the type locality. The crystal structure of weinebeneite has been solved by direct methods and refined in space group Cc to R = 0.043 and Rw = 0.044 using 1341 independent reflections. Weinebeneite is a framework beryllophosphate with calcium and water molecules in the cavities of the structure. The beryllium-and phosphorus- tetrahedra share comers forming a layer consisting of 4- and 8-rings. Two superimposed 4.8(2) 2D nets oriented parallel to (100) and related by translation in b/2 are connected by additional beryllium tetrahedra, giving rise to a framework with an unusual arrangement: five tetrahedra in two three-membered rings share a tetrahedron. Weinebeneite is the first reported example of a framework beryllophosphate containing three-membered rings. Calcium is located in channels parallel to [001], coordinated by three O atoms of the framework and four water molecules. One of the water molecules displays apparent positional disorder over two sites.