You can buy it from the Guild Shop somewhere in Navea. The only problem is that the guild you are in needs to be LVL 3. There are other ways, like using a Pickaxe on the things with a magnifying glass then using a Pickaxe. I was on my way in the mines in the Dwarves' village name and tried to mine the Crystals, and I get mostly Cyan Ores and Amethysts... I barely get Red Agates but at some time later on, it's best to check the wikia but it's going to take a while, so you might as well keep on playing.