Abstract

Ammonioleucite, ideally (NH4)AlSi2O6, occurs as white surface layers replacing analcime crystals in green dolomitized crystalline schist of the Sanbagawa metamorphic belt, Tatarazawa, Fujioka, Gunma Prefecture, Japan.

Ammonioleucite is tetragonal, space group I41/a, a = 13.214(1), c = 13.713(2) Å; c/a = 1.0378; V = 2394.4 Å3; Z = 16. The strongest X-ray powder data are [d in Å, (I/I0),(hkl)]: 5.53(50)(112), 5.43(100)(211), 3.43(40)(004), 3.30(80)(400), 2.955(20)(420), 2.859(20)(323). The mineral is uniaxial positive, n = 1.518(2), ε – ω = very small; single crystals are very small and twinned; color white, translucent; luster resinous to vitreous. Hardness was not determined owing to very fine grain size. Dcalc = 2.24 g/cm3, Dmeas = 2.29(5) g/cm3.

Chemical analysis of a mechanically separated sample, after reducing analcime and dolomite and normalizing to 100%, gave SiO2, 62.66; A12O3, 22.43; (NH4)2O, 8.70; K2O, 4.43; H2O, 1.78; total 100 wt%, corresponding to [(NH4)0.68Ko.19]Σ0.87Al0.89Si2.12O6, based on six oxygen atoms. Differential thermal analysis shows one exothermic peak at 485°C; thermogravimetry shows weight loss between 415 and 550°C. The new mineral is named for the chemical composition and relationship to leucite.

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