What can this possibly be?

[maksim.borisov.201574 (Max)]

Sometimes in a caves i find veins of vanilla minecraft ore. I play with default config pack and with some other mods

[laurynasl (Laurynas Liutkus)]

There are vanilla ores, generated by GT6. Intentionally.

[Gregorius (Gregorius Techneticies)]

Dedicated Stone Layers with Vanilla Ores exist for compatibility reasons, while at the same time making it at the very least more difficult to actually find those Ores, since they are not “everywhere” like in vanilla.

[Demosthenex]

Conveniently omitting the real curse of the vanilla ores…