Chibaite is a new silica mineral discovered from Boso Peninsula, Japan.

{111} twinning of chibaite (size of crystals at the center: 2mm).

Single crystal of chibaite (0.1mm).

Chibaite contains natural gas molecules such as methane, ethane, propane, and 2-methyl-propane (isobutane) within the cage-like silica framework. The framework topology of chibaite is isostructural with the structure-II gas hydrates.

Crystal structure of chibaite.

Chibaite occurs in quartz and calcite veins in tuffaceous sandstone and mudstone of the Hota Group, which is the forearc sediments of Early Miocene age. Chibaite coexists with calcite, quartz, opal, and epistilbite. Minor amounts of pyrite and clinoptilolite have also found in some veins.

Host rock of chibaite. The red arrow indicates a druse containing quartz pseudomorphs after chibaite. The blue arrrows indicate a druse with unaltered chibaite crystals which are shown at the top of this page.

Quartz pseudomorphs after chibaite (white crystals). The semi-translucent cubic crystals under the white crystals are quartz pseudomorphs (most probably) after melanophlogite.