Rollout inflicts damage over five turns, doubling in power for each consecutive hit. The power will reset after five turns or if Rollout is interrupted. The power of Rollout is also doubled if Defense Curl has been used previously by the Pokémon and the user has remained in battle since then. -bulbapedia
so if i gave my pokemon a rock gem the first use it would be 60base power does that mean it will be 120 on the second then 240, 480, 960
or would it go 60, then 60 then 120 and so does the gem effect the whole chain