The Dawn Stone is a Generation IV evolution stone that can evolve a female Snorunt into a Froslass and a male Kirlia into a Gallade. This item can be sold for 
1050 and bought for 10,000.
This item can be found via the Pickup ability by specific Pokémon. In the Sinnoh region games, this item can be found in Mt. Coronet, Route 225, and Route 212 exclusive to Pokémon Platinum. In Pokémon HeartGold and SoulSilver, this item can be found in the Pokéathlon Dome as a prize, as a Bug-Catching Contest prize, at Mt. Silver, or it can be obtained by Biker Aiden on Route 17. In the Unova region, this item is found in Route 10, and Black City exclusive to Pokémon Black.
Strangely, a Dawn Stone evolves Kirlia and Snorunt, who both have evolutions that seem even more masculine and feminine, respectively, but neither of these evolutions need a Dawn Stone. If the player does use a Dawn Stone then he/she gets a evolution that seems to be opposite to the first, gender-wise.