Armor of Rocks (5e Equipment)

Armor (medium or heavy, but not hide), very rare (requires attunement)

While you are wearing this armor, you cannot be knocked prone against your will, and creatures no more than one size larger than you cannot shove you.

While you are wearing this armor, you can cast stoneskin once on yourself, without expending a spell slot or material components. Once you use this armor's property, you cannot use it again until the next dawn.