0.74 ct. Daylight Fluorescent Mexican Opal
Color: Medium Greenish-Yellow
Clarity: Eye Clean
Origin: Jalisco, Mexico
Cut: Oval Brilliant
Treatments: None
Measurements: 7.4 x 5.8 mm
A rather remarkable material. There are plenty of minerals that are fluorescent, that is to say they respond to UV light, either long or short wave. Furthermore, plenty of faceted stones have this response as well - diamonds are often quite fluorescent. But precious few, and essentially none beyond the rarified collector category, are actually daylight fluorescent. That is what you have here, this opal will glow with an bright yellow-green fluorescence in regular old daylight - no special light needed!
Profiled in the Journal of Gemmology a few years back, this material is from a find of hyalite Opal in Jalisco, Mexico. The stone is completely clean and shows a moderate reaction to daylight and a vivid one to longwave UV. Natural light even produces a moderate fluorescence response and gives the stone a fine bright yellow-green color - images one and three (from left) above. As you might expect, exposure to longwave UV light produces an exceptional result - see the above, images 2 and 4. A rare example of this material in a weight that looks quite large for the actual size - Opal has a very low specific gravity so the stone is close to looking like a carat gem of most other species. Loupe clean as well. This material will no doubt become the preeminent example of daylight fluorescence in gems.