While this may look like a natural stone, it is actually layers of enamel paint.
Starting in the 1920s, auto manufacturers began hand-spraying cars to speed up the painting process. Overspray would accumulate in the paint bays, with some of the layers having been baked up to 100 times.
Fordite from the 60's and 70's has the boldest hues, since there was more demand for brightly colored cars at that time, while the enamel from the earlier days of automotive manufacturing tend to have more muted neutrals.
This original piece measures 1-5/16 x 5/8".