2024.12.26 Zircon that changes from blue to brown when exposed to long-wave ultraviolet light

Good morning!

I'm Nori-chan from the GTJ staff.

 

I also want to change... to evolve.

 

In early October 2024, I suddenly introduced several zircons that had a bright blue and green mixed color.

 

At first, I was "attracted by this bright yet mysteriously beautiful color and purchased it." However, I discovered an interesting change when UV light was shined on it during the photography process, which is part of preparing the product for sale. This change is what this article is about: a change in the base color, commonly known as the "tenebrescence effect."

 

Tenebrescence (photochromism) is an optical effect where the base color of a mineral changes by continuously exposing it to long-wave ultraviolet light, which the mineral absorbs. A prime example is hackmanite, which absorbs long-wave UV light to become deep purple, and then gradually returns to its original color. (Note 1)

 

This article is not about the specialized mineralogical content of zircons with interesting changes, but rather about observing minerals, like an experiment anyone can do if they have one.

 

This particular zircon is one of several that were introduced during a live broadcast. It is a zircon with a pale brownish-blue base color. (Note 2)

 

UV light is being applied. It was irradiated for about 1 minute during the live broadcast. This UV light is visible light cut-off specification, so you can feel a significant change even in about 10 seconds.

 

After being exposed to long-wave UV light for about 1 minute, it has changed to a dark brown color. The blue tint has clearly disappeared, and the brown color has come out strongly.

 The sensation is that a brownish-blue (aquamarine) zircon with a metallic luster has changed into a very solid brown zircon. The color change is more pronounced than expected, but because the original color contains a bluish tint, the difference in color change before and after is even clearer.

 

Currently, EGL sorting does not mention "tenebrescence." However, since there is such a significant change, I decided to request a gem identification report from the Gemological Institute of Japan.



The image above shows the inspection results. In the remarks column, it states, "[Tenebrescence (photochromism) observed]." It seems that if the change is too faint, it will not be recognized as tenebrescence, but I believe this batch generally changes to an extent that it is recognized as tenebrescence. (Note 3)
 
 
 


Now, a question arises: "Do other blue zircons change color?" I decided to irradiate the blue zircons I had on hand with long-wave UV light.
 
 
This is a vintage zircon with a slightly stronger blue color. Being blue, it is a piece that was heated to 800-1000°C from Cambodian zircon.
 
 
After applying long-wave UV light for about 30 seconds...




 
It's hard to say it changed, but I could feel a slight difference in color. Somehow, I felt that it absorbed long-wave UV light and became slightly brownish. However, if it's only to this extent, it's highly likely that the Gemological Institute of Japan would not recognize it as tenebrescence. I have 7 blue zircons, and I was able to observe some kind of change in all but one.
 
 
In most cases, the color only gets a slight veil of brown or gray, but the zircons I introduced showed a significant color change from blue to brown, which might be a bit rare to this extent.
 
 
Currently, we only have a few zircons for sale that exhibit such clear color changes that can be called the tenebrescence effect, but we might find more interesting zircons in the future.

 
 
*1 This time, there is no explanation of the principle, only a description of the visual changes.
*2 This zircon is a personal reference stone and is not for sale.
*3 When identifying such minerals, if you request the Gemological Institute of Japan to "confirm tenebrescence and include photos before and after the change if recognized," they will apparently add photos (with an additional fee).