Opal

Opals are multi-colored gemstones, which can have any number of colors. The most expensive ones are black opals, which shimmer with specks of red, blue, green and purple, but many other colorations are possible. Opals are a powerful psionic essence, but this connection is not fully understood by arcanists.

Followers of Odin the Allfather use opal as a symbol of their deity, and his only eye is said to shimmer like the richest opal.