What does a dawn stone do in Pokemon Pearl?

Same as fire stone, water stone and thunder stone. Dawn stone is used to evolute some specific pokemon.

For example, Kirlia (Male) --> Gallade and Snorunt(Female) --> Froslass

Noted that you can only used the dawn stone to evolute a "male" Kirlia into Gallade and a "female" Snorunt to Froslass