Beware that it etches when anything acidic gets on it and that it is more porous and softer than granite.
If you know the few issues it has before you put it in your bathroom, once it's installed you will love it!
Here are some pictures of baths, some use a little and some have a lot of onyx.
This first one is quite amazing. They have used at least four, but possibly six slabs of onyx. The slabs are bookmatched which creates this beautiful pattern on the wall.
This large sink in the photo below is onyx. Crazy right?