I've been scavaging granite(that's right rock), from counter tops, and toying with the idea of making percussion instruments out of them. I've done a little research about Vietnamese Dan tran stone marimbas, Chinese bianqing stone chimes, and various European xylophone lithophones. I wonder if anyone has incorporated rock elements in their drum set? The bianqing form seems especially suited to hanging from a cymbal stand. I think the only draw back is weight, but compared to some things may not be that important.