The Gem on Fire is a special gem event that gives rewards for spending a certain rewards for spending certain gem amounts.
You must spend 50, 1,500, and 5,000 gems for the reward. It lasts from February 22nd, 2015 to February 28th, 2015.
Rewards[]
50 Gems: 3 Fire Fusion Boost Armors
1,500 Gems: Aegis of War+
5,000 Gems: Apocalypse Platemail+