Dirt

Dirt (DI) is a reagent that is in use on Pagan. Dirt is downright easy to find, as one just has to dig a bit into the ground to get it.

Pagan
For the magic school of Necromancy, dirt was used in spells to invoke effects of protection for the Necromancer. Its most famous use of course was the spell Create Golem, which created a creature consisting of dirt.

Ultima Online
When the Stygian Abyss expansion opened, it was found that the gargoyle Mysticism school of magic makes use of dirt as a reagent.