Spheres are glass beads, a little larger than a person's thumbnail with a much smaller gemstone set within its center. The gemstones are able to absorb Stormlight, which makes the spheres glow. Most spheres are also flattened on one side, to keep them from rolling away when set down.
Value:
Spheres are a practical currency. The gemstones within them absorb Stormlight infused during highstorms and they will stay infused for about a week. The Stormlight within them causes the spheres to glow, turning them into a cheap, rechargeable, mobile light source commonly used for illumination everywhere. Such infused Stormlight is also used to power various fabrials.
The size of a gemstone and its type greatly influence its value; the larger the stone, the more Stormlight it can gather and the more powerful its effects will be. Different types of fabrials require different types of gemstones. For example, emeralds are most valuable, since they can be used by Soulcasters to create food.
Stormlight can be measured in chips; gemstones are precisely weighed before being encased in glass. Uncut gems hold less Stormlight than cut gems. Also, Stormlight fades from a sphere over time.
Spheres which run out of Stormlight are called dun spheres. Infused spheres are not worth any more than dun spheres, though sometimes dun spheres are suspect because it is more difficult to see the gemstone inside them, and sometimes a moneylender would have to be brought in to judge the authenticity of a gemstone.
The size of a gemstone inside a sphere determines its denomination. Gemstones come in three denominations: chips, marks and broams. There are five chips to a mark, and four marks to a broam.