ToME: the Tales of Maj'Eyal

Stoning immunity currently does absolutely nothing. There are two ways to apply stoning that I can think of, Stone Touch and Stone Poison, and neither of them check stoning immunity. Stone Touch does, however, check stun immunity. This is fine, as stoning is an incredibly potent status effect (worse even than stun or confusion, just rarer) and it needs to be easily prevented. It'd be nice for Stone Touch to make a note of it in its talent description, however.

Is there even such a thing as stoning immunity?

It exists. One can easily see by making an alchemist; the golem is immune.