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Ice has at least 16 different phases: https://en.wikipedia.org/wiki/Ice

Ice XVII has been predicted: http://www.sci-news.com/othersciences/chemistry/ice-xvii-che...

> The bit about compressibility tickles my mind.

One of my favourites is 'electride' bonding, where you compress a crystal so much that the electrons get squeezed into the gaps (interstices) between atoms instead, essentially making the electrons themselves act as anions.

This is really cool, and makes you wonder what other exotic high-pressure physics waits to be found.

https://www.nature.com/articles/nchem.2254

Following the link that lamename gave about 90 minutes before your comment says that ice-VIII is tetragonal as is ice-IX. The list goes to ice-XVII. See also https://en.wikipedia.org/wiki/Ice#Phases .