# What properties a compound should have to be called an “ice”?

I wonder what compounds are usually called "ice" and what properties do determine it?

I can bring some examples of ice and not.

Not ice:

• $\ce{H2S}$
• cellulose
• sugar
• graphite
• lithium
• solid mercury
• polyvinylchloride
• solid fats
• ...

Known as ices:

• solid water
• solid $\ce{CO2}$
• solid nitrogen
• solid oxygen
• solid methane (?)
• solid ethanol (?)

It seems they all have some common properties:

• Melting point below room temperature
• Transparency
• White or blueish color
• Chystalline structure (?)
• Easy sublimation and high saturation pressure
• Low strength and other mechanic properties
• Low surface friction (?)

Have I missed anything? What is the accepted definition of ices, say in astronomy or chemistry?

• I think "ice" in chemistry is formally used only to refer to water in the solid state. Wikipedia has an astronomical definition for ice based loosely on the melting/boiling points of the material, under which $\ce{H2S}$ would apparently fit. I can't find an official source, though. – Nicolau Saker Neto May 29 '15 at 22:04

Ice is a term usually given to $\ce{H2O}$ in the solid state. Solid carbon dioxide, what is sometimes called "dry ice" is actually a misnomer — although the gas is frozen, it is not truly ice, in the chemical sense. It is called dry ice because instead of melting into liquid carbon dioxide (like actual ice, which is frozen water to liquid water), dry ice sublimates into it's gaseous state, skipping the liquid phase (almost — still goes through liquid phase, but this happens so fast it's basically negligible) entirely.

As for properties, you basically have all of them listed.