Cast on a nearby surface, it explodes for 50 points of fire damage when enemies come near.
Fire Rune is an apprentice level Destruction spell that creates a rune which will explode when enemies come near, causing fire damage and setting targets on fire, dealing 30% of the immediate spell damage, scaling down quadratically over 2 seconds. You can't cast it just anywhere. When you press the cast button, the cross-hair will let you know if you are pointing at a valid surface within range. If it is red, then you can't cast the spell there.