Hey,
I am currently using the 1.21 (neoforge) version and I kinda have the feeling that the ores are not spawning.
I have been playing my current world for around a week and have not found a single ore. I was also not able to find one in a newly created creative world.

I don't know if this is a bug or if I am just unlucky/looking at the wrong place (if so, could you please tell me where the ores spawn?)
This is my mod list btw. https://i.ibb.co/L8QPN45/Screenshot-2.png

*Edit I even installed a x-ray mod and I still was not able to find the ore in my creative world

Hello there, this has been noted
As far for why this happens I'll investigate it during late August.
For now the only way to get these will be via creative or if another ore gen mod is installed and the lava crystal ores are added via them.

Thank you for mentioning it.

Hey,
could you eventually tell me how rare the ore was meant to be?
Because then I at least could trade them for other ores in creative instead of simply giving them to myself, if you get what I mean :).

By this I could trade e.g. 5 diamonds for one crystal.

I'm not sure about the exact exchange range, something like (1 lava crystal = ~ 0.5 diamonds).