A clathrate mineral from Arakawa, Chiba Prefecture, Japan

Abstract

A clathrate mineral has been found from sandstone and mudstone of the Miocene Hota Group in Arakawa, Chiba Prefecture, Japan. Fine fissures are developed in the sediments, some of which are filled with quartz and calcite vein. The clathrate mineral occurs in quartz vein and druse in the quartz vein. While most of the crystals are quartz pseudomorph after the clathrate mineral, we found some fresh crystals. Rietveld and MEM analysis of X-ray powder diffraction data have been performed since all the crystals have pseudo-merohedral twinning. The crystal system is tetragonal and the lattice parameters are a=13.7190(9), c=19.349(1). The framework of the clathrate has the MTN type structure. Raman peaks of methane molecules in guest sites in the cages are observed.