Leylines

Magic as we know it, and spells by direct association, is the metaphysical effects and manipulations of a chaotic and bewildering effect of arcane energy natural to the world. But the world is vast, unrepeating, and especially flawed. Leylines are the best example of this, and the best proof that magic is a manipulated force, especially in the hands of mages. Leylines are best described as strips or spots in the world that may not be physically cracked but still seeps that raw arcane energy, potentially twisting any who reside near it for too long, and especially acting as an accelerant for spellcasting. Some places have had adverse affects in population, such as people being transformed by the raw magic of these leylines, while others casting seemingly mundane spells have drastic results. Not too much is known about the leylines, and not all locations are known of where they are, though some have been recorded. 

Ley Crystals

In addition to the leylines and the curiosity surrounding them, even more dangerous and unknown are the ley crystals. Formed in large clusters of rocks that could potentially be mistaken for some other type of crystal, these crystals are raw magic in solid form, and therefore can be extremely dangerous and unpredictable in the wrong hands. Not much is known about them and their abilities, but they can have serious and deadly side-effects for any who possess them while casting magic. 
It has been discovered that they have two states: a dormant state and an active state. In an active state, they remain safe to handle generally, although they can cause various symptoms among arcane users, including nosebleeds. Any damage to the stone, however, can cause any number of magical explosions or effects to happen, causing destruction or death in some cases. In their dormant state, however, they do not seem to be any threat and can possibly even be destroyed safely. Currently, there is no known way to manually change the state of a crystal from dormant to active, though it is possible that an explosion of one piece of ley crystal can deactivate others in the vicinity.
It has also been noted that the explosion of said ley crystals can create an anti-magic field where magical effects and spells no longer work within a certain area around the area of the reaction. The duration of the field is currently unknown.

Manifestation

Leylines cannot be seen, so the average cannot find a leyline, however spellcasters, especially those of the arcane, can sense when a leyline is near. As for the ley crystals, they have a slight glow to them that can be used to distinguish them in a dimly lit cave.

Type

Metaphysical, Arcane