Magic is found in the form of small crystals that grow in abundance in the tunnels and caves near the surface. The larger high-yield crystals, which have to be mined
The smaller low yield mana crystals grow in the caves and some tunnels near the surface of Sheyol. These can be both mined and farmed, but are usually farmed, with some farms being major industrial scale operations. These are more than enough for the needs of most magics, with crystals ranging in size from as a grain of rice up to the size of a finger bone. They can be broken or ground down into smaller crystals (although with difficulty as the crystals are incredibly tough) and are used as portable fuel and power sources as well as for all manner of magic. It is not uncommon for the magically inclined to and ingest, inhale, or inbibe powdered mana, although the effects can be at times unpredictable and there is a movement in public opinion to condemn such behaviour.
For the high yield magics, mining is a more accurate way of describing the extraction process. It is not without it’s risks though, and mining is often considered one of the more dangerous jobs in the city.
The high yield mana crystals grow strongest close to the surface. Which means that there is always the risk of breaking through to the surface, and since the crystals cannot be broken without explosive results once they reach the size of a tennis ball. When a large crystal is found, the whole thing must either be removed intact or left in position. On more than one occassion, a large mana crystal has been removed, only to cause a cave-in: Especially dangerous when it is difficult to tell how far from breaking the surface you are, for the surface of Sheyol is unhelpfully jagged and uneven, with dips and valleys across it. Whether this is local or across the whole world is unknown, but scarcely makes a difference.