Vibration Isolation for equipment using granite?

I recently visited a high-end audio salon and in the course of discussions with the owner, we discussed the large number of black granite 18x18" blocks he had against the wall. He said that he dealt with a granite retailer to make them from scrap granite pieces from kitchen installations, etc. He said that all equipment (amps, pre-amps, cd platers, DACs, streamers, turntables, etc.) all seemed to benefit from having them underfoot, even on quality equipment racks. It made me wonder if this was true or snake oil? I have my equipment (except power amp) on a Standesign equipment rack with each MDF shelf resting on small aluminum cones that "isolate" it from the steel frame. Question is, does this just add mass which would or wouldn't dissipate the vibration energy or does it work (maybe on another principal). And would sandstone or marble drink coasters, especially with cork soles) work better? Has anyone tried ay of this? Thanks in advance.