I recently started a campaign playing an oracle, to try something new. I have the Stone Mystery and at 1st level have the rock throwing revelation. Now, in the description it says "You can hurl rocks up to two categories smaller than your own size. The range increment for a rock is 20 feet, and you can hurl it up to 5 range increments. Damage for a hurled rock is 2d4 for a Medium creature or 2d3 for a Small creature, plus 1-1/2 your Strength bonus." The DM seems to think that means all these rocks have to be (playing human=medium size-2 categories) Tiny-sized rocks, akin the the size of a bowling ball. I believe this is just the maximum size rock I can throw, but can throw smaller rocks with the same effect. Which is correct?
Although I can kind of see the DM's point: I threw a rock at an enemy bard, hit for max damage which, at 1st level, instantly decapitated her. Hard to see a tiny pebble doing all that.
DogBone
I'd agree with the GM: the size of the rock determines the base damage. The wording isn't clear, but this interpretation meshes well with the rest of the game, where weapon size determines base damage (large longsword dealing 2d6, but an ogre with a medium-size longsword only gets the 1d8, as would the halfling using the same sword).
Quick calculations for weights:
From the weights of Small Water Elemental (34 lbs) and std. Small Earth Elemental (80Lbs) and using a 1/8 per size reduction I would go with a Tiny Object could be between 4.5 to 10 lbs and a Diminutive Object between 0.5 and 4 lbs.
I would allow "Innapropriate size weapon" (-2 att.) using a Diminutive rock for a Medium Thrower or Tiny rock for a Small Thrower (-2 att., full-round action with 2 hands free). Or even a Fine rock (under 0.5 lbs, 2d2) for a Small Thrower (with the -2 att.) would be nice for an old reference to halfing rock throwing.
Not sure about use of Small rock (35-80 lbs, 2d6!) for a Medium Thrower (-2 att., as a full-round action with 2 hands free) but it would look cool!