Water may be the most abundant substance on the planet's surface but it continues to throw up surprises. The latest discovery is that sandwiching water between two sheets of graphene leads to it freezing at room temperature to form two-dimensional square ice crystals, a hitherto unknown phase of ice.
Previously, 17 phases of stable ice were known to exist – all with their own characteristic molecular arrangement, packing density and symmetry. Unusually, the newly discovered square ice has a symmetry that's completely alien to water molecules and different from all other known ices.
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