Though our collection isn't very extensive, this is without a doubt, the most unique piece we have. First of all, the color patterns across the different wave lengths are beautiful. Second, the piece grows noticeably brighter the longer it's exposed to shortwave, and it isn't phosphorescent. Third, the hemimorphite changes color the longer it's exposed to shortwave, starting as a greenish grey and becoming a stunning shade of blue. Fourth, the hemimorphite is tenebrescent. The tenebrescence is currently under study at CalTech, as it may be the first non-disulfide mineral to exhibit the behavior.
We would never have stumbled upon this material had we not attended a Fluorescent Mineral Society chapter meeting. One member showed a specimen of hemimorphite that changed in brightness and color, so we tracked down a few samples. This one is the best by far, both with color and brightness. Moral of the story, join the FMS and participate!
Shown in LW, MW, SW immediate, SW 30+secs, Natural, and Natural after SW. Hemimorphite is blue in SW 30+secs, fluorapatite is greenish in all wavelengths, and tarbuttite is yellow/orange in LW.
Note: the seller claimed that smithsonite is in this piece and is perhaps the material that fluoresces orange.