Rockhorn Summit / Hot, Hot, Hot Quest

[Sfubi]

This lava rock is not accessible for collecting lava rocks but the one at rendtail's entrance is usable for the hot, hot, hot quest. Why?

[Madnex]

Because in that instance, someone else has already collected that one.

[Bigboyblue]

I have had this happen to me as well. Running solo. No one has got to it before me. For some reason I can't collect it.