Storage gems

Some gemstones naturally absorb elemental energy, and thus can be used by elementals as additional storage for when the amount of energy they need exceeds what their body can deliver.

The preferred types of gems for each element are: emeralds for ether, rubies for fire, and both diamonds and saphires for frost. While any translucent green, red, orange, yellow, blue or white stone is capable of absorbing an element, none of them do it nearly as efficiently as the aforementioned group.

Soulstones are special yellowish green gemstones that can be used to store souls.