Glass—the primary currency and commodity of Erj. Glass is generally traded in quantities of small, smooth stones which have no predetermined value; rather, they are individually rated for their purity. Common, lower-grade glass is used in the production of weapons and tools, while skilled glaziers utilize purer grades to craft mirrors and spectacles for the wealthy.

It is rumoured that the nomadic Suneaters have become so adept at glasswork that they have learned to capture the light of the sun itself to wield as a weapon, via complex arrays of mirror and lens.