I have used Granite for many Years as Sub Plinths for Audio Equipment on Racks and as a Cabinet Speaker Sub Plinth.
I find I prefer the sonic that has been created when using it, when the Granite is a Sub Sub Plinth or a Sandwich Material in a Build up of Materials to create a Plinth or Sub Sub Plinth.
For Speakers I always uses a Spike Coupling and Pneumatic Footer to create some suspension.
On the equipment Rack, I always use Cork as the Isolation footer for the Granite when in a Sandwich or as a Sub Sub Plinth.
Other Materials used in conjunction with the Granite will have a selection of Footers tried out to discover which tidies up the sonic to a standard I am happy to experience.
Today, my usage of Granite is seemingly being superseded by the use of Phenolic Resin Densified Wood Board Materials, such as the Board Materials from the Brands Permali or Panzerholz.