text: what is the fifth state of matter?   it could be glass (or amorphous solid) which is considered to be a state or phase between solid and liquid.  if you're looking for something beyond plasma, that question gets pretty tricky to answer because it's quite subjective. you've got quark-gluon plasma, superfluids and loads of other stuff. some of them haven't existed since the big bang. some are theoretical. a lot depends on how you define state so take yer pick!  by the way, contrary to what the answer above says, carbon dioxide can form a liquid phase; just not at atmospheric pressure. at high pressure (over 5 atmospheres) it will form a liquid phase. this to do with triple points and all that sort of thing.  edit: a triple point is where gas, liquid and solid phases exist in thermodynamic equilibrium. triple points are part of a phase diagram and phase diagrams describe how a substance's phases behave under different conditions.   water's triple point occurs at 0.01 c, 0.006 atm. it definitely does not form a super critical fluid under those conditions. are you sure you're not confusing the triple point and the critical point (which is where liquid and gas cannot be distinguished: this is the start of the super critical region)?  don't believe me? check the links. the last one is for some lozenges for that nasty cough you've picked up ;) ...