The Flame Crystal is a building in Dragon City that allows your dragons to earn revenue faster. You are limited to four crystals per game and each crystal has a certain radius which covers a certain amount of area. If your habitat is within that radius your dragons will gain 20% faster income rate. You can stack all crystals together for a total of 80% increase but if they are not within the radius your habitat will not get the booster effect.
How to use
Just build and place near a Flame habitat for the item to take effect. Please keep in mind that if you do not see it’s effect then that means your habitat is not within the radius and you need to place it closer. The more you stack the better and this does not improve breeding rates. It also does not improve your attacks.