Scientists recently discovered a rare phenomenon previously believed to not occur on earth. Trapped inside a diamond, they found naturally occurring, high-pressure ice – more commonly identified as ice-VII. Oliver Tschauner, professor of geoscience at the University of Nevada, explains that when chemical bonds are subjected to pressure, the bonds tilt towards each other and compress. However, water ice bonds change shapes, which is why the usual ice-I has a hexagonal shape. Apply a little more pressure and you get ice-II which has a rhombohedral molecular structure, up until ice-VII which has stable cubic structure.
Ice-VII, which is 1.5 times denser requires a high amount of pressure and was believed to be only found on the icy moons of our solar systems. Such high pressures are only found near the earth’s mantle, but down there it is too hot for this ice to have formed. Water in diamonds is common, but finding water ice intact is a rarity.