Oh boy, that is beautiful.

A couple of things that I've heard on this forum is that sanded grout is needed, regardless of finish of the tile, if the grout space is 1/8" or greater. It is because of shrinkage of the grout, and I think the sand mechanically stabilizes this process. The Latacrete line reportedly has very small and uniform grains of sand and it is not supposed to scratch.

Second there are differing opinions on this, but how about epoxy grout? It is reportedly stain resistant. I also have read that people have had success with applying as DIY's. I am sure that the floor would be a perfect place to use the epoxy. I don't know why it wouldn't work with your onyx, but maybe a pro can chime in and give some feedback.

Last, I can only guess that your onyx needs sealing, as does marble and travertine. I hear people list different sealers that they've used, etc. on this forum but I don't know which is the best.

I know this reply is rather speculative, but hope it is of some help.

Hi enduring, do you know what brand for epoxy grout is good? that sounds very intriguing. even if i cannot use it on the onyx,i do have another bathroom with ceramic tiles that i can use it in..

i did read on another forum that onyx does not need to be sealed, but there has been a lot of differing advice on it. so it is difficult to tell what to do.. i guess i might have to just do some experimenting on my own.

thanks for the ideas!