Stone Form

CON 13, wild shape ability,

As a standard action, you can spend one of your
uses of wild shape to assume a stony and rocklike form. While
in this form, you gain a +4 bonus on Fortitude saves against
poison. Your natural armor bonus becomes +4 (replacing any
natural armor bonus you normally have, though you retain
any enhancement bonus to natural armor).
You also gain a slam attack that deals bludgeoning damage
equal to a morningstar appropriate to your size (2d6 points
for Large characters, 1d8 points for Medium characters, 1d6
points for Small characters).

Without this feat, a druid can only use wild
shape to assume the form of an animal, plant, or elemental.

As a standard action, you can spend one of your
uses of wild shape to assume a stony and rocklike form. While
in this form, you gain a +4 bonus on Fortitude saves against
poison. Your natural armor bonus becomes +4 (replacing any
natural armor bonus you normally have, though you retain
any enhancement bonus to natural armor).
You also gain a slam attack that deals bludgeoning damage
equal to a morningstar appropriate to your size (2d6 points
for Large characters, 1d8 points for Medium characters, 1d6
points for Small characters).

Without this feat, a druid can only use wild
shape to assume the form of an animal, plant, or elemental.

You can use wild shape to assume a rocklike form