Original paper

Weinebeneite, CaBe3(PO4)2(OH)2 ∙ 4H2O, a new mineral species: mineral data and crystal structure.

Walter, Franz

European Journal of Mineralogy Volume 4 Number 6 (1992), p. 1275 - 1284

32 references

published: Dec 15, 1992
manuscript accepted: Mar 30, 1992
manuscript received: Sep 29, 1991

DOI: 10.1127/ejm/4/6/1275

BibTeX file

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Abstract

Abstract 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 - 4l dmeas.= 2.15(4) g/cm3 and dcalc.2.17 g/cm3. Optically, weinebeneite is biaxial positive but nearly uniaxial with 2Vγmeas. < 10° ; nα = 1.520, nβ = 1.520, nγ = 1.530 (589 nm); Z: c - 42° in acute angle β. Weinebeneite is monoclinic, a = 11.897(2), b = 9.707(1), c = 9.633(1) Å, b = 95.76(1)°, V = 1106.8(3) Å3 and Z = 4. The three strongest lines of the X-ray powder diffraction pattern are [d (Å), (hkt), I]: 2.513, (2¯23), 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 O7.88(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 corners forming a layer consisting of 4- and 8-rings. Two superimposed 4.82 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.

Keywords

weinebeneiteberyllophosphatecrystallographycrystal structureframework