Nolzeite, Na(Mn,square)(2)[Si-3(B,Si)O-9(OH)(2)]center dot 2H(2)O, a new pyroxenoid mineral from Mont Saint-Hilaire, Quebec, Canada

摘要

Nolzeite, Na(Mn,square)(2)[Si-3(B,Si)O-9(OH)(2)] center dot 2H(2)O, is a new mineral found in altered sodalite syenite at the Poudrette quarry, La Vallee-du-Richelieu, Monteregie (formerly Rouville County), Quebec, Canada. Crystals are colourless to pale green and are acicular with average dimensions of 5 mu m x 8 mu m x 55 mu m. They occur as radiating to loose, randomly oriented groupings within vugs associated with aegirine, nepheline, sodalite, eudialyte-group minerals, analcime, natron, pyrrhotite, catapleiite, steedeite and the unidentified mineral, UK80. Nolzeite is non-pleochroic, biaxial, with n(min) = 1.616(2) and n(max) = 1.636(2) and has a positive elongation. The average of six chemical analyses gave the empirical formula: Na-1.04(Mn-1.69 square(0.24) Fe0.05Ca0.02)(Sigma=2.00)(Si2.96S0.04)(Sigma=3.00)(B0.70Si0.30)(Sigma=1.00)O-9(OH)(2)center dot 2H(2)O based on 13 anions. The Raman spectrum shows six distinct bands occurring at similar to 3600-3300 cm(1) and 1600-1500 cm(1) (O-H and H-O-H bending), 1300-1200cm(1) (B-OH bending), 1030-800 cm(1) (Si-O-Si stretching) as well as 700-500 cm (1) and 400-50 cm (1) (Mn-O and Na-O bonding, respectively). The FTIR spectrum for nolzeite shows bands at similar to 2800-3600 cm(1) (O-H) stretching, a moderately sharp band at 1631 cm(1) (H-O-H) bending, strong, sharp bands at similar to 650-700 cm(1), similar to 800-840 cm(1), and similar to 900-1100 cm (1) (Si-O and B-O) bonds. Nolzeite is triclinic, crystallizing in space group P with a = 6.894(1), b = 7.632(2), c = 11.017(2) angstrom, alpha = 108.39(3), beta= 99.03, gamma = 103.05(3)degrees, V = 519.27 angstrom(3), and Z = 2. The crystal structure was refined to R = 12.37% and wR(2) = 31.07% for 1361 reflections (F-o>4 sigma F-o). It is based on chains of tetrahedra with a periodicity of three (i.e. a dreier chain) consisting of three symmetrically independent SiO4 tetrahedra forming C-shaped clusters closed by BO2(OH)(2) tetrahedra, producing single loop-branched dreier borosilicate chains. The chains are linked through shared corners to double chains of edge-sharing MnO5(OH) octahedra. Nolzeite is a chain silicate closely related to steedeite and members of the serandite-pectolite series. Paragenetically, nolzeite is late-stage, probably forming under alkaline conditions and over a narrow range of low pressures and temperatures.