Abstract
AbstractBosoite (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/cm3. The empirical formula (based on 2 O apfu and guest molecules assumed as CH4) is Na0.01(Si0.98Al0.02)Σ1.00O2⋅0.50CH4; the end-member formula is SiO2⋅nCxH2x+2. Bosoite has the space groupP6/mmm, with the unit-cell parametersa= 13.9020(3) Å,c= 11.2802(2) Å,V= 1887.99(6) Å3andZ= 34. The crystal structure of bosoite was refined by single-crystal X-ray diffraction and converged toR1= 4.26% for the average model andR1= 2.96% for the model where all oxygen sites are split.
Highlights
Silica clathrates are zeolite-like materials constructed of pure silica framework structures with small cage-like voids
The order of crystallisation of melanophlogite, chibaite and bosoite observed in the present study indicates a decisive role of guest molecules on their crystallisation
From the previous studies on syntheses of these clathrasils, the presence of large molecules matching in size to the largest cage in the crystal structure is considered as a necessary condition for their crystallisation
Summary
Silica clathrates (or clathrasils) are zeolite-like materials constructed of pure silica framework structures with small cage-like voids. A list of Raman shift positions of the hydrocarbon molecules measured in bosoite are given in Table 1 along with those in the free gas state, in chibaite, and in melanophlogite for comparison.
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