An item that boosts the Special Defense of a Pokémon. Zink also boosts a Pokemon's happiness. In adition, the effort value of that stat boosts bye 10.
It is P9800 at the Slateport City Marketplace in Pokémon Ruby/Sapphire.
In Pokémon HeartGold/SoulSilver Zinc is sold for P9800 and is worth 1 Battle Point.