If held by a Heatran, the Heatranite allows it to Mega Evolve into Mega Heatran if its Trainer has a Key Stone. A Trainer can only have one Mega-Evolved Pokémon at any given moment.
Prior to the release of Mega Dimension, an internal file of Pokémon Legends: Z-A referred to the IDs of a nonexistent Heatranite, along with the Darkranite and Zeraorite, indicating they were originally implemented in the base game but were cut.
In addition, their internal item IDs are not grouped with the other Mega Stones introduced in Mega Dimension, instead being where they would be if they were introduced in the base game of Pokémon Legends: Z-A; in the Heatranite's case, it is between the Froslassite and Darkranite.
