This image, for example was creating only with stones:
Here is another, a landscape, with a lapis lazuli sky.
Here, a more primitive example:
In other cases, artists would take an existing stone as a kind of background and paint a few figures on them:
Upstairs, there was a display of the kinds of stones used; the Medici were obtaining precious stones from all over the world, although Italy itself is a major source for the stones.
Needless to say, there was virtually no one else there. Who needs the Uffizi?