I’ve carved as much around the lava lake as I dare. I’ve harvested granite, diorite, andesite, and obsidian (which is really really hard and takes a long time to mine correctly unless you like breathing shards of volcanic glass) but no diamonds.
Not a single one.
I’m down to the core bedrock here, so it’s not like they’re deeper. At this point I’m just assuming there aren’t any diamonds near this lake and I’m moving on.