Most of the 100 tables I've made have included semi-precious focus stones.  A few interesting ones havenet. The edges of the ones using thin slabs of Lyons sandstone, like the one above, are protected with grout and a thin steel band.

However I found five thick slabs of Indian sandstone a few years ago that don't need the rims.  This stone was cut from a mountain in India; loaded onto a a ship to San Francisco as ballast; and shipped to a stone yard in Lyons Colorado where I found them.  I have two of thes slabs left.  I'd love to make them into a table for you!