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A great piece of fluorescent sodalite (hackmanite) with bright red-orange fluorescence under shortwave. This specimen is extremely tenebrescent with a white matrix to really highlight the color change.
The material from this locality is probably the winner in the color-change department. We don't have much of this deeply tenebrescent material left.
Upon exposure to SW UV the sodalite on this piece changes color to a deep purple - in seconds! Expose it to a bright white light (UV free halogen or LED spotlight held directly on the rock) and it reverts back to its natural color almost immediately. The LW fluorescence is knock-your-socks-off bright.
The animation shows the color change (tenebrescence) after exposure to longwave and shortwave UV.
The tenebrescent color of a piece of hackmanite can range from a light pink to a deep "grape jelly" purple. The time it takes the tenebrescence to fully develop is also quite variable, as well as the wavelength to which each specimen will react. Shortwave UV (254nm) generally is the most effective wavelength in causing tenebrescence, but some specimens will also react nicely to longwave (350nm) or even obscured sunlight (cloudy days). Any bright UV-free light source will "bleach" the color and return the mineral to its previous color (sunlight, even though it has a UV component, will also bleach most hackmanite – probably due to the intensity of the other wavelengths).
365nm UV light is often called "blacklight". Before the advent of longwave UV LEDs, blacklight fluorescent tubes, (the kinds used in hippie days to light up psychedelic posters) were the standard longwave UV light for our hobby. They were not very powerful but they did light a large area.
Enter 365nm UV LEDs
First, an animation showing the difference between the UV flashlight we recommend (365nm filtered UV flashlight) versus unfiltered 395nm UV flashlights we see many folks carrying around at shows. So. much. visible purple light. We selected a bunch of rocks as a demonstration. Took pictures of them under his flashlight without the filter and then with the filter.
A major component of rock collecting (for us) is simply getting out in nature. A buddy dragged us out to a very remote area here in middle Tennessee to hunt for fluorescent green agate. Since we consider ourselves pure "Glow Hounds" we weren't anticipating any glow rocks, just the beauty of the area, but we brought our UV lights anyway.
