Opal!

I posted this concept in Wattles' youtube community page and it got a surprising amount of likes/kind comments so I thought I'd try posting it here. I drew some textures for it but I can't figure out how to insert an image... the opal itself is a spherical gemstone with a vibrant gradient of light yellow to green to blue to purple. Opal ore generates underwater in beaches and ocean biomes. My initial idea was that it has the efficiency of iron and durability of diamond, but some people in the comments gave me some wonderful ideas. I think Opal tools and weapons should be more effective underwater than on land. Prismarine could also be crafted with opal and stone. It's a relatively lesser known fact that prismarine changes color over time, which could be related to opal's natural vibrancy. Maybe chunks surrounding ocean monuments don't generate opal, to show that whatever civilization built them mined all the opal to build their temples.