Abstract

Garronite-Na, ideally Na6(Al6Si10O32)·7–10H2O, a new mineral species, was found in the Mont Saint-Hilaire quarry, Québec. It occurs in vugs in sodalite syenite. The crystals are transparent to translucent, pale yellow in color, with a white streak and vitreous luster. Crystal aggregates are botryoidal masses up to 1.5 mm in size. The mineral is brittle with a good {011} parting. Associated minerals include aegirine, natrolite, gmelinite, and gonnardite. Garronite-Na is monoclinic, space group I2, with unit-cell parameters refined from single crystal X-ray diffraction data: a 9.990(2), b 10.032(2), c 10.036(2) Å, β 90.11(3)°, V 1005.8(7) Å3, and Z = 1. Electron microprobe analyses give (average of eight with ranges): Na2O 14.28 (10.38–18.55), K2O 1.10 (0.51–3.07), CaO 0.04 (0.01–0.11), MnO 0.02 (0.00–0.09), BaO 0.09 (0.00–0.44), FeO 0.02 (0.00–0.07), Al2O3 26.89 (25.71–28.96), Nb2O5 0.04 (0.00–0.10), SiO2 46.71 (42.65–49.32), TiO2 0.00 (0.00–0.02), H2O 10.73 (10.22–11.22) (determined by crystal structure analysis), total 99.92 wt.%. The empirical formula, based on the crystal-structure analysis and ideally showing 16 (Si + Al) and 32 O atoms in the framework and 7.3 H2O groups is: (Na5.650K0.286Ca0.009Ba0.007Mn0.003Fe0.003Nb0.004)∑5.960(Al6.468Si9.532)∑16O32·7.3H2O + (O0.67). Garronite-Na is biaxial positive, α = 1.489 ± 0.001, β = 1.492 ± 0.001, γ = 1.496 ± 0.001, 2Vmeas. = 75(3)°, 2Vcalc = 82(7)°. The strongest eight reflections of the X-ray powder-diffraction pattern [d(obs.) in Å (I) (hkl)] are: 7.098 (79) (011, 110), 5.026 (32) (002, 200), 4.101 (77) (112, forumla, forumla, 121), 3.172 (013, 031, 130, 310), 2.904 (14) (forumla, 222), 2.685 (64) (123, forumla), 1.9669 (14) (015, forumla, 341, 510), 1.7213 (11) (forumla, 053, 350, 433). The Mohs hardness is ∼4; D(meas.) = 2.19(2) and D(calc.) = 2.071 g/cm3. The structure has been refined to an R index of 0.056 for 2952 unique, observed reflections. The structure is a Si/Al–O framework like that of gismondine with Na atoms and H2O groups in the cages.

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