title: New silica clathrate minerals that are isostructural with natural gas hydrates.
abstract: Silica clathrate compounds (clathrasils) and clathrate hydrates are structurally analogous because both materials have framework structures with cage-like voids occupied by guest species. The following three structural types of clathrate hydrates are recognized in nature: cubic structure I (sI); cubic structure II (sII); and hexagonal structure H (sH). In contrast, only one naturally occurring silica clathrate mineral, melanophlogite (sI-type framework), has been found to date. Here, we report the discovery of two new silica clathrate minerals that are isostructural with sII and sH hydrates and contain hydrocarbon gases. Geological and mineralogical observations show that these silica clathrate minerals are traces of low-temperature hydrothermal systems at convergent plate margins, which are the sources of thermogenic natural gas hydrates. Given the widespread occurrence of submarine hydrocarbon seeps, silica clathrate minerals are likely to be found in a wide range of marine sediments.
authors.affiliation: Department of Earth and Planetary Materials Science, Tohoku University, Aoba, Sendai, Miyagi 980-8578, Japan. MOMMA.Koichi@nims.go.jp
authors.forename: Koichi
authors.initials: K
authors.lastname: Momma
authors.forename: Takuji
authors.initials: T
authors.lastname: Ikeda
authors.forename: Katsumi
authors.initials: K
authors.lastname: Nishikubo
authors.forename: Naoki
authors.initials: N
authors.lastname: Takahashi
authors.forename: Chibune
authors.initials: C
authors.lastname: Honma
authors.forename: Masayuki
authors.initials: M
authors.lastname: Takada
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Furukawa
authors.forename: Toshiro
authors.initials: T
authors.lastname: Nagase
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kudoh
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis; D005579:Fossil Fuels / Q000032:analysis*; D019015:Geologic Sediments / Q000737:chemistry*; D005844:Geology; D006838:Hydrocarbons / Q000737:chemistry; D008958:Models, Molecular; D012822:Silicon Dioxide / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D002247:Carbon Isotopes; D005579:Fossil Fuels; D006838:Hydrocarbons; D012822:Silicon Dioxide