Going up two tiers of chisel (rusty->steel) didn’t seem to provide me anything. I am pretty sure it took two taps per rock before(due to mining level) and still took 2 taps after.
Provide some abilities to:
Decrease time to get new rocks(items go away faster and new rock is rolled out quicker)
Roll out more than 1 rock at a time, as one reward is being presented let the player click the others.
Bring out entire piles at a time that can be mined all at once.