Question: what are unova stones used for?
Answer: Pokémon Go's Unova Stone is an special evolution item that allows you to evolve Pokémon from Gen 5 just like the Sinnoh Stone. Unlike the Sinnoh Stone, however, the Unova Stone won't be used to evolve Pokémon from previous generations. Instead, it will be used to complete many of those introduced in Gen 5.