Does anyone know?
So far our fissure/uw group has found several rubies and sapphires. They seem to be much rarer than ectoplasm blobs and obsidian shards though. We've found over 200 ectos and shards combined; during that time we've only found 3 rubies and 4 sapphires.
I don't think there is currently anything you can craft with them. Just save them, and when there is something to craft with them, you will be in the lead.