The Adamant Orb, an type-enhancing item, is found in Pokemon Platinum and Pokemon Diamond, but can be traded for in Pokemon Pearl. When the Adamant Orb is held by Dialga, it increases both Dialga's Dragon and Steel type attacks by 20%. This makes a Dragon Claw from Dialga much more dangerous, including STAB Dragon Claw gets.
 Pokémon Diamond, Pearl & Platinum
However, in Pokemon Platinum, the Adamant orb can only be found after gaining HM08 Waterfall. Then, in Mt. Coronet find the Waterfall in B3F? and surf up it, going into another cave to find this orb and the Lustrous Orb. A Stone Plate is hidden in the rock separating these two items.
 HeartGold & SoulSilver
The Adamant Orb can be obtained in the Sinjoh Ruins Event. If Dialga is chosen the baby Dialga will emerge holding the Orb.