Ah, thanks for clarifying. All stone would indeed be a joke. I had been arguing with the guy about fan blades for a while, starting with him saying all wind turbines must have blades made of fiberglass or they won't work. I said the fanblades should be made of metal on small ones.

I figured there's no way he's saying a dynamo costs more energy to produce than it can ever generate, and there's no way he's saying adding a mount makes it cost more to produce than it can ever generate, so he must be saying metal fanblades have the same cost-to-produce issue as fiberglass.

Stone isn't that hard to shape uniformly, but it won't have all the helpful properties you want, and it will probably need the fan assembly/bearings replaced more often, but if metal fanblades are really too expensive to produce then it still would solve that problem which is just an extreme example to prove bare material cost can't be the problem