ToME: the Tales of Maj'Eyal

It could also use a name that's different from the t4 Earthen Power skill, but that's more of a cosmetic problem.

Eldritch Stone is up there with Fears as one of the worst locked categories in the game. It gives a single skill with terrible damage on a 12-turn cooldown, plus some status effects that will never, ever hit against anything that matters because Stone Wardens tend to have terrible, no-good, very bad spellpower due to wearing shields instead of a staff and armor instead of robes.

I think that some (probably more than one, but certainly not all) of the following should be implemented:

1. Make the various abilities separate skills, with their own cooldowns.
2. Make points invested in the tree reduce the cooldown.
3. Make it an unlocked category.
4. Make the tree scale with physical power instead of spellpower.
5. Remove the percent chance from the status effects (they still won't hit a whole lot; see above).
6. Increase the damage significantly.
7. Add a healing effect.
8. Make using the skill take Body of Stone and/or Deeprock Form off cooldown (if they're on cooldown).
9. Add crit multiplier to the hit and/or to other skills.

I'd go for removing the percent chance, have the duration scale(3+TL) for Disarm/Silence(so it starts a bit lower than it is now, but ends up higher at cap), and allow every part of it to critical check separately. (I forget if it does the last, but I want to say no.)

Removed the chances and made the durations scale.
Effects check for the higher of physical or spell power.

I however am bemused by you thinking it's a low damage spell.
Sure it does it's damage over 6 turns, but with a naked test character level 50 with 100 magic if all talents are maxed it does well over 600 damage to a big cone, and that is without a crit. Considering most spellcaster spells are designed to do around 200 base at most.

Stone Wardens don't usually have 100 magic. Heck, Stone Wardens don't always even have 60 magic. They also don't tend to have much in the way of spellcaster gear or spellcrit, unless the player is doing some kind of weird wannabe-archmage build that would nerf all of her defensive skills.

Also, bear in mind that in return for a category point and up to 20 class points, you get ONE skill on a 12-turn cooldown. By "most skills" you mean stuff like Flame, right? Those do about 1k-ish damage with gear on a crit, so the equivalent for Eldritch Stone if it scaled the same way (it wouldn't, for the reasons I just gave) would be 3k-ish on a crit. That's just straight-up awful for what it costs.

For a look at the way Eldritch Stone behaves in a real-life test, check out this guy. Note that, at level 50 and with full endgame gear (including Limmir's and some vault items), he's getting sub-200 damage over 6 turns for the first skill (with only one point invested, so double that for what a real investment would look like). He has 67 spellpower, which is a lot for a stone warden, and 48% spellcrit. To get that, he's chosen to wear light armor (Molten Skin) instead of the massive or heavy armors he would need to leverage Stone Fortress properly. He's maxed Magic instead of Strength or Willpower, so he won't do anything like as much damage in melee as he should, and his vines won't hit as often. And he's forgone Deeprock Form, Celestial/Light and Spell/Stone.

He's sacrificed all that for a tree that would average perhaps 2k damage over 12 turns, maybe 3k if we're being generous, with a 20 point investment (which he hasn't made).

That said, making it scale with physical power will be a huge buff, perhaps even enough to make it viable. As you can see from my long-winded explanation, a lot of the reason why it's so lackluster is the fact that hybrid nature of Stone Warden makes it quite hard to get a credible amount of spellpower.

I honestly never thought it was low damage.

It's not incredible damage, but it's a huge spread cone. Comparing it to Fireflash is somewhat unfair, too, as that's on a mage class with a ton of AoE focus, and possibly the best area control spell in the game overall.

Considering that it also does status, it's not really bad at damage. If it can crit, and the status is more substantial, it seems fine to me.