well, here is another rare and unusual stone. When I was younger I dabbled in jewelry making as every good Indian does.lol One of the things that we used to sharpen and burnish our tools were graver stones. These usually were made out of natural beryl or sintered rubies. They always came in small sizes usually about 1in x 2 or 3 inches and about 1/2 inch thick at the most. Well, I forgot all about them until I joined this site. The trigger was finding out that Spike was a retired goldsmith. So, I emailed him a few months ago and asked him if he knew if any suppliers made large stones that could be made into sharpening stones. He got back to me and said that his supplier hadn't seen any and that if they could find it that it could be quite expensive. He also wasn't sure how good the stones would be as sharpeners as they are very fine and would probably polish instead of giving you that bite you want in a knife edge. Being the stubborn person I am I spent the last few months searching for a supplier and found almost exactly what I wanted, but a little bit better. This is an extremely hard 3k ruby side and a much softer 10k agate side. for some reason the agate side photographed dark, that streak is actually white and is not a crack, just a natural feature of the stone.
This stone is a combo stone
half synthetic sintered ruby 3k
half natural agate 10k
200mm x 50mm x 25mm