1.93 ct. Daylight Fluorescent Mexican Opal
Color: Medium Greenish-Yellow
Clarity: Eye Clean
Origin: Jalisco, Mexico
Cut: Custom Triangle
Treatments: None
Measurements: 9.9 x 8.9 mm
A relatively new and 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 intense 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 eye clean and shows a vivid reaction to daylight. Under completely incandescent lighting, the stone is a light stray yellow shade, but indirect natural light produces a moderate fluorescence response, but direct sunlight sets the stone aglow and gives you a stone with an almost 'highlighter' yellow color. As you might expect, exposure to longwave UV light produces an exceptional result. So, in the above images you are seeing, from left: daylight, total incandescent light (the least amount of color possible), longwave UV, daylight again and, finally, longwave UV again. A rare example of this material in a weight of over 1 carat - given the growth habit of these, larger stones are extremely uncommon. Plenty of colorless Opal is fluorescent with a UV lamp, but here it is that daylight ability that is exceptional and quite dramatic. This material will no doubt become the preeminent example of daylight fluorescence in gems.
As an interesting note, these grow as botryoidal masses and you can indeed see a bit of the structure of this looking closely at the stone. It appears like radiating fluid lines, perhaps best seen in the last two images. Fascinating!