It is a small sample of cooled lava which seemingly attracts anything that is of worth to its current owner. It is first seen in possession of Rohan Kishibe, who had collected two samples of the rock. However, one is destroyed by Jodio Joestar who takes the remaining sample with him.
Rohan keeps one of the samples in a safe, next to his diamond. The Lava Rocks are extremely precious and Rohan is confident that the two small samples in his possession are the only ones in existence. Jodio crushes one of the samples to blackmail Rohan, leaving only one left. Rohan secretly reveals to Jodio that he can become extremely rich if he handles the Lava Rock with care, due to it containing a hidden "mechanism". Rohan lets Jodio take the remaining sample with him, but warns him not to tell anyone about its properties, not even his allies.
The appearance of these Lava Rocks are fairly innocuous, being dark and porous much like any ordinary cooled lava. The remaining sample has a distinctive tetrahedron shape and is small enough to fit in one's hand.
Abilities and Powers
Jodio and Dragona discover that the Lava Rock gathers valuable material toward it, such as Rohan's diamond, bank notes, and Pink Dark Boy artwork. Even a $20 bank note is valuable enough to be brought back to the Rock.
Jodio infers from the fact that the Lava Rock was kept isolated in a safe together with the diamond that the trigger of the Rock's power is either contact or close distance. Through experimentation, Usagi, Dragona and Jodio discover that somehow, circumstances will conspire to make anything of worth that has touched the Rock travel back to it. The way objects return to the Rock varies from them mysteriously slipping from a container and finding themselves near the Rock, to more complex strings of events. For example, a bank note placed under the Rock which is then used by someone else to buy food, returns to the group via Paco Laburantes having his drink refunded by the staff because of a bug accidentally flying into his drink.
The ability to have precious items be drawn to the Lava Rock happens automatically. This means that it can happen at an inconvenient time. For instance, while Dragona was aiming to make the Rock touch a few precious wristwatches to eventually make them return to it, one wristwatch is immediately drawn towards the Rock while the watches were laid out on a table in the shop Dragona was testing the Rock in, which catches the attention of the clerk and security guards since they noticed one went missing.
Among items that can be drawn back to the Lava Rock, precious foodstuff is notable. Valuable food that was ingested by someone or something can still be drawn to it, and even force whoever ate the food to go towards the Lava Rock. Usagi uses this property to his advantage to trap a couple of cats who had eaten some caviar belonging to Rohan. However, Usagi presumes this mechanism no longer works once the food was digested.