Fact Check

Does Hyalite Opal Glow Green When Exposed to UV Light?

The gem is known to contain traces of uranium.

Published May 11, 2021

Updated May 12, 2021
Image Via Flickr
A rare gem known as hyalite opal glows green when exposed to UV light due to natural traces of uranium.

A video shared to Reddit in early May 2021 appeared to show a piece of what you might call real-life kryptonite — a brightly glowing, green-hued hyalite opal that the original poster of the video claimed got its vibrancy from uranium. At the time of this writing, the video had been upvoted more than 66,000 times.

Snopes readers asked our team to verify whether it was true that hyalite opal glowed bright green under ultraviolet (UV) light, and we determined this to be true. Hyalite opal is a gemstone that was first characterized by German geologist Abraham Werner in 1794 while its uniquely fluorescing characteristics were described by Otto Flörke in in 1973 — and new classifications of the vibrant gem have been discovered in the decades since. In 2013, a new type known as Mexican hyalite opal was discovered in the Mexican State of Zacatecas, a geologically active region near the Sierra Madre Occidental Volcanic Province.

“This material possesses spectacular color behavior, appearing near-colorless or pale-to-moderate yellow in incandescent light and vivid greenish-yellow to yellowish-green in indirect sunlight,” wrote researchers describing the find in The Journal of Gemmology.

Hyalite opal is composed primarily of silica and is created through a series of volcanic processes deposited over millions of years from “super-volcanoes” similar to those found in Yellowstone National Park. During eruptions, some lava that chills in a large depression known as a caldera create siliceous volcanic glass that is then shattered into tiny shards and settles with pumice fragments and volcanic ash to make what is known as “tuff.” Over time, these tuffs condense and mix with other materials, including silica and uranium, and settle into layers below the Earth’s surface. Silica and uranium are eventually incorporated into emanating vapors and interact with emerging water from hot springs, and as they descend, eventually combine and redeposit as opal, chalcedony, or quartz.

These trace amounts of uranium in the silica create a radioactive element that is both visible under UV light and detected with a Geiger counter, as seen in the below video shared by Indiana jeweler Moriarty’s Gem Art:

Opal is generally known for its fluorescence when put under UV light, but Mexican hyalite opal is unique in that it can also fluoresce in natural light. These types of gems are “truly rare” and after their discovery nearly a decade ago, they began attracting attention because of their “noticeable change” from light colors to vivid green in indirect sunlight — a unique property that granted them the nickname, “Electric Opal.”

The radioactivity level of hyalite opal is in background levels and does not pose harm to human health, but some items that include uranium can emit low levels of radiation for thousands of years, according to the U.S. Environmental Protection Agency (EPA). This has been found to be the case in American products that were made to contain certain radioactive materials for their color-inducing or fluorescing properties before scientists largely understood the health effects of radiation.

Take “Vaseline glass.” For centuries, glassmakers would use small amounts of uranium to create dish ware named for its yellow or green tint that, when put under a UV light, caused the glass to glow.

Image of a Vaseline-glass cup that can glow under a black light. National Museum of American History/EPA

“Uranium has been incorporated as a coloring agent in glass since its discovery as a new mineral in 1789. The use of uranium for coloring glassware was especially popular from about 1910 to 1940 for light yellow Vaseline glass and dark green Depression glass,” noted the Health Physics Society, a nonprofit science organization. “These pieces of glassware are now collectors' items found in antique shops everywhere.”

But the EPA largely prohibited U.S. glassmakers and ceramic producers from using radionuclides like uranium for color in 1970, according to the EPA.


[May 12, 2021]: This article was updated to clarify the discovery of hyalite opal.

Madison Dapcevich is a freelance contributor for Snopes.