If you're talking about the small, rugged rocks, then I don't think you can. The only rocks I know you CAN move/break are the huge boulders made for Strength.
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You can break rocks by using the move Rock Smash.
get the HM strength, and teach it to a Pokemon
There is no TM that can Break rocks in Pokemon leaf green there is however in HM that breaks rocks called RockSmash
HM06 Rock Smash
Any Pokemon able to learn the HM strength can move boulders. To shatter rocks you need the HM Rock Break.