Gas hydrate

Structure of a gas hydrate embedded in sediment.

A layer of gas hydrate (white), deposited in marine sediment.

A gas hydrate is ice with gas enclosed in its molecular structure. Gas hydrate should not be confused with ice that contains bubbles of compressed gas. In such a hydrate, a gas molecule is enclosed in a clatratic (cage) structure of ice molecules.

All gases except helium, hydrogen, and neon can form gas hydrates.

They are produced under conditions of high pressure and low temperature and in the presence of gas; they are destroyed when they are in conditions of low pressure or high temperature.
For example, methane hydrates are destroyed at more than -15 °C and 1 atmosphere of pressure.
Under high pressure conditions (500-2000 atmospheres) they can form at warm ambient temperatures.