Structure of Methane Hydrate
Methane hydrate has the approximate formula CH4.6.2H2O. In the structure each methane molecule is enclosed within a cage of 20 water molecules which are arranged in a pentagonal dodecahedron. In the picture below, the H atoms have been omitted for clarity. Methane molecules are represented by a single grey sphere.
There are large natural deposits of methane hydrate - it can be found beneath oceans at depths of >300m and also under permafrost. It can cause serious problems in natural gas pipelines - if the gas is wet and the temperature is low, methane hydrate can form and block the pipeline. In order to prevent this, pipelines have to be insulated or chemicals added to prevent the formation of the hydrate.