Crystal Chunks in Genshin Impact are an important resource. You can refine them at a Blacksmith to create Mystic Enhancement Ore to upgrade weapons, and you will also need plenty of it to build other weapons in the game.
Crystal Chunks can normally be found in mountain areas of the game and inside caves, but there are two areas where this resource is pretty common that make excellent farming spots.
The first area you are likely to farm these properly is around Stormterror’s Lair after you hit the relevant point in the story to get access to it. You can find Crystal Chunks all around the main lair area. The second area is Qingyun Peak, a mountainous area in Liyue. Both will have plenty of Crystal Chunks in them if you do a bit of exploring.
To break Crystal Chunks, you will need to use heavy weapons like the Claymore, bombs such as Amber’s second ability, or Geo abilities can also make quick work of them. If you are just using normal swords, you will need to hack away for quite a while to get them to break.
Expeditions can also be a great way to passively farm up Crystal Chunks. You can send characters you don’t need in your party to explore certain areas, and they can come back with all manner of resources. There is also a good chance you will just find these blue crystals while you are out exploring the world, so make sure you keep your eyes open and farm any of them that you see. Don’t instantly convert all of them in Enhancement Ore, as you will need some as a raw material to build better weapons.