Not wishing to hijack the Granite thread,

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looks like resin or fiberglass

How large of a hole?

Probably regular bits for small holes and carbide grit for larger holes.

It is possible a natural stone ... hard to tell from the photo. I recently removed an old marble countertop and had a similar mesh on the bottom side. My guess on the marble I had was the mesh was to reinforce any natural cracks in the slab.

Here's a marital tip-no matter what the counter is made of, do not c-clamp a reloading press to it.

Ditto on cleaning stainless guns in the dishwasher and washing bore snakes in the clothes washer.

Cultured marble. Nasty dust. I’ve cut them with fine-tooth sawzall. Or maybe it was a grinder?

Thanks everyone.