Gems and precious stones hold magical power, and those trained in the traditions of Petromancy can evoke those magics for their own use. Each type of gemstone has its own unique frequency of magic, allowing those practiced in the Petromantic tradition to channel power through it and create a specific type of effect.
Scholars believe that Petromancy somehow taps into the energies of Apex, the Far Realm of Order, using the crystalline matrix and facets of a gemstone as a lens to make that plane’s inimical power into something controllable by mortals. This hasn’t been conclusively proven, but the fact that Petromancers gain a slight but noticeable increase in control and efficiency with their use of magic in areas with strong connections to Apex lends credence to the theory.
The nations with significant numbers of Petromancy practitioners have their own distinct styles of the magic. Vauldan Petromancers insist that clear and finely-cut stones grant the best combination of power and finesse, while Tomarrans overwhelmingly prefer rough stones, or better yet stones that are still part of their original rock matrix. Iskaldur stone mages, meanwhile, prefer simple cabochon or ovoid cuts for their stones, especially those with stars within them, and the Sunderwyl Petromantic tradition has developed an avid belief that the sheer size of the stone is what matters, finding ways to mediate any flaws or imperfections in a stone via wire wrappings and Technomantic devices.
If you wish to play a Petromancer, collect an assortment of precious and semiprecious stones to use as your character’s talismans in spells and rituals. Either wear them in jewelry, mount them in ritual objects, or just have a collection of stones that you pull out of their container and use as a spell focus when you perform a ritual. (Please do not spend too much money on this — we’re perfectly happy if you take a red plastic or glass “gemstone” and call it a ruby, so don’t break your bank account in an attempt to be perfectly authentic in the materials you use.)