STRUCTURE OF ICE

Ice Ic

Ice Ic forms from the vapor below about -80°C and appears to be a metastable form of ice, although it has almost exactly the same density as Ice Ih. Ice Ih does not change to Ice Ic at very low temperatures but Ice Ic reverts readily to Ice Ih when warmed above -80°C. Ice Ic may form in extremely high clouds and some halo features not readily explainable in terms of hexagonal ice have been attributed to Ice Ic (http://www.uwgb.edu/dutchs/PETROLGY/Ice%20Structure.HTM).



Structure of Xenon Hydrate


Schematic description of one of the possible gas hydrates: the water molecules build up an ice crystal (a solid structure, then) composed of regular dodecaedres, and each dodecaedre traps a gas molecule.

As you can see the crystal structures of ice Ic and xenon hydrate are different.