Gen 6 all duel types are gotten rid of an replaced by a single type depending on the combination, here are a few.

Water / Ground = Mud type
Fire / Rock = Magma type
Rock / Steel = Mineral type
Normal / Flying = Bird type
Water / Poison = Pollution type
Electric Steel = Machine type
Dark / Ghost = Spirit type
Fighting / pshycic = Monk type
Bug / Steel = Gasoline type