A silicate creature that resembles a large, irregular, generally rounded rock with a horn on the bottom of its body

A rock bat is a silicate creature that resembles a large, irregular, generally rounded rock with a horn on the bottom of its body. It floats by emitting a glowing gravity ray from gem-like growths on the sides of its body. Its rocky hide and floating ability give it a respectable armor class. A rock bat attacks by dropping directly down on its prey. On a natural 20 the victim is impaled by the rock bat, receiving 1d6 points of damage each round until either the victim or rock bat is slain.