Starting at level 4, every so often a small swinging padlock icon will appear on a gem. If this gem is not matched, it will become a Locked Gem on the next turn. Locked Gems cannot be moved. However, they can be matched like any other gem, or destroyed by Flame or Lightning Gems at usual.
There can be no more than 8 Locked Gems on any board. Locked Gems are destroyed at the end of each level.
Locked Gems do not appear in Zen and Blitz mode.