Crystals and Mundane Armor

[Chester]

Can an augment crystal (ie restful crystal) to armor that isn't masterwork?

[Darrin]

Can an augment crystal (ie restful crystal) to armor that isn't masterwork?

No. MIC p. 221:

"A least augment crystal functions whenever attached to an object of at least masterwork quality, even if the object itself has no magical properties."

There may be something of a RAW loophole in that you can attach a lesser or greater augment crystal to a suit of armor that has an enhancement bonus via the magic vestment spell, but a sharp DM is probably not going to let that fly.

[MaxiDuRaritry]

A warforged's armored body is technically not even masterwork, but it can be magically enhanced, so in this one case, a +1 or greater warforged armored body can take an armor crystal even without being masterwork. As to whether or not an unenhanced one can be? Probably not. At least, not unless you use logic to state that the body armor in question is masterwork by inference.