Bosoite, A New Silica Clathrate Mineral From Chiba Prefecture, Japan

Bosoite (IMA2014-023) is a new silica clathrate mineral containing hydrocarbon molecules in its crystal structure. Bosoite can be considered structurally as a silica analogue of the structure-H gas hydrate, where guest molecules are trapped in cage-like voids constructed of the host framework. The mineral occurs in the Miocene tuffaceous sedimentary rocks at Arakawa, Minami-boso City, Chiba Prefecture, Japan. Bosoite is hexagonal, and it crystallises as an epitaxial intergrowth on chibaite crystals, with the {0001} of bosoite parallel to octahedral {111} form of chibaite. Crystals are colourless and transparent with vitreous lustre. The calculated density is 2.04 g/cm(3). The empirical formula (based on 2 O apfu and guest molecules assumed as CH4) is Na-0.01(Si0.98Al0.02)(Sigma 1.00)O-2.0.50CH(4); the end-member formula is SiO2.nC(x)H(2x+2). Bosoite has the space group P6/mmm, with the unit-cell parameters a = 13.9020(3) angstrom, c = 11.2802(2) angstrom, V = 1887.99(6) angstrom(3) and Z = 34. The crystal structure of bosoite was refined by single-crystal X-ray diffraction and converged to R-1 = 4.26% for the average model and R-1 = 2.96% for the model where all oxygen sites are split.