Scheelite

Scheelite is a mineral useful for ultraviolet transparency testing. Shown here is a skarn, a metamorphic rock with a crystalline surface, with scheelite and other minerals under normal visible light. "Garnet-pyroxene-molybdenite-scheelite skarn 2," photo by James St. John. Licensed under CC By 2.0.

Article: Ultraviolet Testing and Gemstone Identification

Credit: James St. John