I tried honing a marble vanity top and the surface of the top is powdering and I cannot seem to to get the shine back. What’s going on?

Are you sure its a marble top? It sounds like you tried to hone a cultured marble top. Cultured marble may look like real marble but is actually a plastic resin that is coated with a very thin layer called a gel coat. If you try to hone cultured marble it will remove the gel coat and you will end up a powdery mess.

TIP Cultured marble can be improved by applying a wax coating. Carnauba based car waxes seem to improve the shine. Apply several coats and buff with a electric polisher and a lambs wool applicator.