This lava rock maybe inspired by the Red Stone but it seems to operate like Milagro Man, but instead of money, it seems to attract things based on what the person wielding subconsciously covets like how Dragona really liked that Gold Watch and the item was trying to avoid being captured by the Store Guards. Its certainly a connection on Jodio's philosophy on mechanism which is inspired by Fate itself. Perhaps this will be a test of Jodio's philosophy given that his greatest desire is to become very rich. I'm getting ahead of myself but Lava Rock maybe difficult to extract safely hence why the "Owner" is eager to claim it at any cost.
I know the gang is referring to the Mafia alot, but I'm still hoping for the Rock People to reappear again. They could be minor antagonists for all I care, I just like the potential, Araki could expand in the story and keep it connected to Part 8, especially concerning Jodio's parentage.