Continental rocks are older than oceanic rocks. The continents have been continously growing over millions of years and adding the oceanic sediment to their margins over time.
All depends on the size you want. Most rocks are sold for $10 and $20 rocks . it's rare to be sold for anything lower or higher. In a crack rock you get only half the weight of the rock in cocaine....
It depends on how big the originial un-crushed rock was. If you specify a weight for the original rock then maybe a formula can be devised for this question. However, anything that is solid and then...