This is an opal from the Takarazaka region. I cracked open a nodule today for the first time in a while. I can see a shimmering play-of-color opal peeking out from the crack. This will be listed as a play-of-color nodule. I've heard that mining has ceased and it's no longer possible to collect these. Apparently, they were miraculously formed from the seabed millions of years ago. I took the photos with my phone under a lightbulb. This was given to me a while ago and is a valuable item. I was surprised to see how expensive they are when I looked at mineral sales sites. Since this is a personal listing, I'm offering it at a lower price. Please check the size of the mineral with a ruler.