Gem Seam

Gem seams are a type of impassable terrain that can be mined for gold in Dungeon Keeper and Dungeon Keeper 2. It mines more slowly than a gold seam (25 gold/per dig in Dungeon Keeper 2), but never runs out of gold and never changes to another type of terrain. Room walls cannot be placed on gem seams.
A Gem Seam is neutral. It can be neither claimed nor fortified. So be careful if you mine a gem seam close to an enemy dungeon.