Im not sure if anything like this has been posted before, and im not sure if this was the right place to post the question, ao i apologise in advance if i make anyone angry... at the beginning of the year my lecturer posted the challenge to find another compound which, like water, was lese dense in its solide state than in its liquid state. now this question is not for marks or extra credit or anything (just a slab of beer), and at the beginning of the year i became rather obsessed with the challenge...many hours searching the net. However, exams came around and i have only just recently thought about it again. the best thing i could come up with at the time was silicon dioxide, it had been mentioned on many sites, but i couldnt conclusively provide evidence eg. Data sheets showing density both as solid and liquid.... so i post the question, can anyone here think of a compound, which like water has a solid state that is more dense than its liquid state...?