Just smashing all the rocks in the desert mine at the moment. The Omni geodes give a reasonable chance at iridium ore. Sometimes you stumble upon Iridium Nodes too.

Ah, thank you. That's great to know. I was farming for iridium and chanced upon that so I was pretty pleased.

Each type of geode has a different loot pool.  Omni geodes can contain any mineral as far as I'm aware.

I got one of those and donated it to the museum, did I fuck up?

http://i.imgur.com/4zCa98F.png

Unsure if the drops from the geodes are based on which mine you dig in, but the batch I got the shard from was from the skull dungeon.

For those who can't seem to find Mystic Stones or Iridium Nodes, it may be worth just breaking regular rocks along the way.

You can get Prismatic Shards from Omni Geodes