Marble or Granite shelfs in a hifi rack?

Mknowles, I mentioned that Granite has that ringing. I didn't say that marble does. I think that marble, being a sedimentary rock, has more in common with limestone, than with granite. Therefore, I would guess that marble would not ring much, or at all. However, it does break very easily, if it is not supported fully from the bottom. As such, I would not expect it to be suitable for shelving on an audio rack.

As far as granite ringing, I know that 3/8" thick definitely does, and I haven't done specific tests on other thicknesses. I have read some material that referred to granite TT bases causing unwanted resonances.

Stone is a terrible choice for Hi Fi racks, you would get better sound with cardboard and save money

I have had terrific success with thick granite, particularly
in combination with other isolation devices. I've also
tried the 4" in thick maple which I feel is even better.

To take the subject admittedly but interestingly off-topic for a sec, I once bought an unusual gift of a windchime made from shards of a particular kind of obsidian (natural volcanic glass) that forms in 'fingers'. Dangle these pieces from monofilament and they ring like bells, with a very pleasing overtones structure.

Anyway, although I have not experimented with this myself, many audiophiles and manufacturers seem to prefer one of manufactured granite or marble substitutes that are used in kitchen countertops, such as Fountainhead (hope I got that name right?). Presumably these are fabricated using bonding resins that act as damping agents.

At one time I had four slabs of 3 inch machined Granite and used them under amps, preamp and turntable. After experimenting with them (damping) in every possible way, I sold them. Could never completely eliminate the signature they imparted into the music.

Next I tried Neuance shelves, then 2 inch marine plywood shelves laminated with decorative finish, finally settling on 3" solid maple butcher block. I had the top and face covered with Westinghouse brand laminate in a semi flat gray color.

The Maple butcher block probably has a signature as well, it's just more natural sounding in my system. Perhaps trial and error is required for each person to get it right.