The term "cryocrystal" refers to any crystalline solid formed by condensation and freezing of a material that is gaseous at room temperature and atmospheric pressure.

Examples are the RGS (rare gases solids) solid neon (s-Ne), solid argon (s-Ar), solid krypton (s-Kr, which I think we really ought to call "kryptonite") and solid xenon (s-Xe). (Helium is solid only at high pressure and very low temperature.)

There are also numerous "molecular" solids such as solid nitrogen (N2), solid oxygen (O2), solid methane (CH4), "dry ice" (solid CO2) and so on.

One thing all cryocrystals have in common is that they are held together by weak van der Waals forces (otherwise they would condense and freeze at much higher termperatures); they are therefore known as "van der Waals solids" and are (especially the RGS) among the simplest and best understood of all solids.

Jess H. Brewer
Last modified: Sat Nov 29 10:32:59 EST ±