This item has two different tasks for which you need to compolete, depending on the game. In Ruby, Sapphire & Emerald, you need to return this item to Professor Cozmo. In return, you'll get TM27 - Return In FireRed & LeafGreen, Bill asks you to deliver it to Lostelle's father on Two Island In Pokémon Omega Ruby & Alpha Sapphire, this item is obtained in Mt. Chimney and goes through various aesthetic changes as you play through. At the end, it is eaten by Rayquaza and allows for it to Mega Evolve at any time, regardless of hold item.
A meteorite found at Meteor Falls.
A meteorite that fell from space onto Mt. Moon long ago. It is very lumpy and hard.
A meteorite that you got at Mt. Chimney. Some sort of pattern has risen to the surface, and it's shining with seven colors of light.