Hyalite opal from the Chalk Mountain Mine, in Spruce Pine, North Carolina, provides a classic example of uranyl-activated green fluorescence, and is one of the most brightly fluorescent minerals. This specimen consists of glassy hyalite opal (Opal-AN) on a light-colored granite pegmatite matrix. The opal shows brilliant green fluorescence under short wave UV, and a bright green response under long wave also. The size of this specimen is 10.2 x 8.9 x 6.3 cm, and the area of fluorescent opal is approximately 6.4 x 4.4 cm.
Interestingly, because the hyalite contains trace amounts of the element uranium, it is slightly radioactive.
As shown above, the hyalite opal fluoresces a brilliant green under short wave UV (254 nm).
Under long wave UV (365 nm), the hyalite shows a bright green/yellow response.
Same specimen shown under visible light. Note the crust of hyalite opal on the surface of the granite pegmatite host rock.