Tumbled willemite is a zinc silicate mineral that is known for its fluorescence under ultraviolet light Fluorescence: When exposed to ultraviolet light, willemite emits a bright green light. Some of the light continues to shine even after the UV light is gone. This is because ultraviolet light boosts electrons in the willemite's structure to higher energy states, and then the electrons emit green light as they fall back to a lower state. Color: In daylight, willemite can be colorless, white, gray, or red. Value: Willemite with a bright, intense green fluorescence is usually the most valuable. Cabochon-style willemite can be valuable, ranging from $10 to $50 per carat. Sources: Willemite is found in the Franklin and Sterling Hill zinc mines in New Jersey, as well as in Chihuahua, Mexico, and Namibia.
