Here are photos that show the onyx in a countertop application. You might want to contact the designer directly on this job to see its pros and cons. Click on the name of the photo for additional details including designer contact info




This last photo is of a quartzite called Lumix that looks very similar to onyx in case you do decide to change materials.

My knowledge of onyx is limited to gemstones. I know that it is considered brittle and large pieces of onyx (in jewellery) are prone to shattering if it is knocked hard by another hard sufrace...like a wall, coffee table, cement, etc.

I believe this is one of the reasons you are being cautioned against using it as a work surface. If you used a glass surface, you would still have to figure out a way to mount the glass so that the onyx underneath is protected. You would have to use tempered glass (like the stuff in microwave ovens) which will add to the cost. The 'protection' will add the price of a "glass" counter top to the price of your onyx counter top.