Daylight fluorescence is a phenomenon where some fluorescent minerals show a noticeable color change under sunlight, due to the UV component of the sunlight causing a bright fluorescent response seen in daylight. Notable examples of minerals that exhibit daylight fluorescence include some colorless hyalite opals which appear green under sunlight, and certain willemite specimens from Franklin, New Jersey, which also show green daylight fluorescence. Probably the most notable example of daylight fluorescence can be seen in the beautiful green fluorite specimens collected from the Rogerley Mine, Weardale, England. The following photographs show such a specimen:
Short Wave UV (254nm)
As seen in the above photograph, fluorite from the Rogerley mine shows a beautiful blue fluorescent response under short wave UV.
Long Wave UV (365nm)
Under long wave UV, above, this fluorite responds with brighter, more intense, blue fluorescence, very difficult to accurately depict in a photograph. In fact, this is some of the most brightly-fluorescent fluorite from anywhere.
In addition to being a spectacular fluorescent mineral, this fluorite is also stunningly beautiful under visible light. The above photograph was taken under a panel of white LEDs, and shows the deep green color that is typical of Rogerley fluorite. The more gemmy specimens make outstanding visible light display pieces.
The final photograph, above, was taken outside in open shade during the day. Comparing this image to the photo taken under the white light of the LEDs (with no UV component), a significant color shift to blue can clearly be seen. This is due to the UV component of the sunlight causing blue daylight fluorescence.
The size of this specimen is 10.0 x 7.1 x 5.3 cm, and it weighs 319 grams.