I picked this hone up for free today! I dunno what it is, but I can tell you what it isn't. it doesn't have the feel of a black ark or the slurry. It feels like a less glassy C12k. It has a feeling of very fine abrasion, it is very hard and was glass-like before I lapped it. Slurry stone doesn't produce slurry like a BBW or a Coti, much slower and it scratches the surface. In real life it is a very light green color with darker streaks running through it. It does have one tiny inclusion that looks like a red garnet out of a BBW. Ive taken pictures with water,dry,slurry, and with a tape measure if it helps. It was about 5/8" to 11/16ths thick before I lapped it.