Crimson Agate was introduced when the snowy Dragonspine area first got added to the map. There are many useful items and hard-to-find resources hidden in the world of Genshin Impact like Crimson Agate. It is a crystal found in the coldest area of Mondstadt.
This crystal can only be found in the area and its surrounding areas, there are a total of 80 available for collection. Dragonspine is a fairly large area but fortunately, there are a considerable number of Teleport Waypoints, which are relatively close to the crimson agate.
Crystals usually float in the air, but sometimes they can also be found in chests. Treasure chests with a bright red halo contain crimson agate.
An image from GenshinImpactMap that shows where to find Crimson Agate:
How to Use Crimson Agate in Genshin Impact
The main purpose of this red crystal is as a offering to the Frostbearing Tree. By using stones as offerings, you will level up in the tree and get rewards. At level 8, you will unlock the Crimson Wish, which is a commission that rewards you for getting more Crimson Agate.