What do I clean my onyx table with to prevent scratches and marks?

Onyx is very soft and susceptible to scratches and stains. You need a glass or plastic cover. If stains penetrate, you cannot remove them easily.

Read these links:

Marble & Onyx Care & Cleaning (http://www.pak-marble-onyx-ways.com/HTML%20pages/care-and-cleaning-marble-onyx.aspx)

How to Care For Your Onyx Countertops (http://onyxcountertops.org/onyx-countertop-care-maintenance/)

Mark

I would go with a Microfiber cloth and warm water if it's only dust on the table, though you need to be careful with cleaning products, some can damage the table.