Frost agate

Frost agate, also called a frost stone, was an agate with white frost-like appearance over the base color.

Description
These rare ornamental stones were usually tumbled and polished to a beautiful glassy finish. A master lapidarist could cut the fragile stone in facets so that at each point where facets met (such as in a polyhedron cut, the shape of a d20), a "snowflake" of white "frost" appeared. Frost agates were often enchanted to be luckstones. Low quality stones were treated like other agates, powdered for use in draughts and potions. A typical stone had a base value of 10 gp.