Not ice -- not necessarily cold at all and capable of being boiling hot without visibly boiling. It is exceedingly slippery and difficult to walk across without stumbling and sliding helplessly across its surface. Can prove to be terribly effective when used in the construction of funnel-traps. Will shatter metals. Vulnerable to psionic attack -- enough psychic energy will cause it to fragment and dissolve into a smoky mist. Northern barbarians collect it from lakes found beneath dragon's caves and use it during ritual performances.
What have you heard of?