Starting in skull cavern is your best approach, focus floors below 100 where mystic stones and iridium nodes appear more frequently. Bring plenty of bombs and staircases, and dont forget luck-boosting food like spicy eel for better drops. The quarry can be interesting, look for those dark blue mystic stones with their 25% drop chance

Check the volcano dungeon on ginger island first since theres a guaranteed shard in the summit chest, and while youre at it crack any omni geodes you find at clints shop. Fighting serpents and mummies in skull cavern is decent especially with a burglar ring, and setting up a rainbow trout pond with 9+ fish gives you a small daily chance

For some passive options, fish treasure chests with magnet bait when you have time, and keep an eye out for those rare meteorites since they drop shards pretty often. Good to know that once you reach true perfection youll get daily shards from a special statue, but for now focus on those mystic stones and iridium nodes, since theyre your most reliable source

Remember to hold onto your first shard for that galaxy sword upgrade, its absolutely worth it for better mining runs