Diamonds - How to find? The conditions for their appearance

After walking around the volcano, I finally found JUST ONE strange diamond growing next to the 7z capsule on that high platform in the cave with all those booms and crystal slime. This is the only one I have found so far. Its ore deposit also seemed to be gone when I returned later to see if it would give me another one. Where did you find the strange diamonds? I would like to compile a list of possible spawns, as well as understand what biomes and conditions they spawn in. Can someone help me?