If you walk into a dust cloud, you'll either find a Gem, Evolutionary Stone, or encounter a rare Pokémon. Gems can only be found this way. They can also help out your Pokémon in battles by powering up their moves with the right gem.
List of Gems
|#529||Drilbur||Wellspring Cave, Chargestone Cave, Mistralton Cave, Twist Mountain|
|#530||Excadrill||Challenger's Cave, Victory Road, Giant Chasm|