Diamond: The lesser of three diamond types, which includes Canary Diamond and Blue Diamond.
Clerics use diamonds to bring a person back from the dead. In Neverwinter Nights 2, there is no material component requirement but some people like to roleplay that it does.
Raise dead: Diamonds worth at least 5,000 gold are consumed as a cost of casting the spell. This is a fifth-level cleric spell.
Resurrection: Diamonds worth at least 10,000 gold are consumed as a cost of casting the spell. This is a seventh-level cleric spell.
True Resurrection: Diamonds worth at least 25,000 gold are consumed as a cost of casting the spell. This is not currently implemented in game.