Hi Roger,

My experience with onyx is that it has been easily polished.That being said there are many variations of the stone.Depending on the wear of the surfaces you are working on keep in mind that onyx is soft and you shouldnt need to cut to deep to get a good refinishing effect.

It can be polished cold or hot-I prefer somewhat hot(dry polishing)  using small amounts of powder until factory finish is reached.Stay mindful of the load on the pad so you can control the heat.