When this spell is cast, the affected creature gains a virtual immunity to any attack by cut, blow, projectile, or the like. Even a sword of sharpness cannot affect a creature protected by stoneskin, nor can a rock hurled by a giant, a snake's strike, etc. However, magical attacks from such spells as fireball, magic missile, lightning bolt, and so forth have their normal effects. The spell's effects are not cumulative with multiple castings.
The spell blocks 1d4 attacks, plus one attack per two levels of experience the caster has achieved. This limit applies regardless of attack rolls and regardless of whether the attack was physical or magical. For example, a stoneskin spell cast by a 9th-level wizard would protect against from five to eight attacks. An attacking griffon would reduce the protection by three each round; four magic missiles would count as four attacks in addition to inflicting their normal damage.
The material components of the spell are granite and diamond dust sprinkled on the recipient's skin.
High-Level Campaigns Book Note[]
Stoneskin: This spell is subject to considerable abuse by player characters. Multiple stoneskins placed on a single creature are not cumulative. If two or more stoneskin spells are cast on the same creature, roll normally for the number of attacks each spell protects against. If a new spell protects against more attacks than the present spell does, the recipient gets the benefit of the increased protection; otherwise there is no effect. The caster does not necessarily know how many attacks the spell can shield him from.
Stoneskin protects only against blows, cuts, pokes, and slashes directed at the recipient. It does not protect against falls, magical attacks, touch-delivered special attacks (such as touch-delivered spells, energy draining, green slime, etc.), or nonmagical attacks that do not involve blows (such as flaming oil, ingested or inhaled poisons, acid, constriction, and suffocation). Stoneskin lasts for 24 hours or until the spell has absorbed its allotment of attacks.