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Minerals under shortwave uv light

Fluorescence, Tenebresence and Phosphoresence

A while ago, I wrote about my microplastic research and my plans about staining plastics with fluorescent Nile Red. Some equipment was ordered, when the coronavirus broke out and the shipping status of the equipment became uncertain. After 2 months waiting, the uv flashlight was still not on its way, but stuck in the US as air cargo was basically at a halt. Finally, when the package was put on a boat instead the flashlight arrived a couple months ago.

Meanwhile, I had been searching for Nile Red to purchase as an individual. Most web shops that sell it in Europe immediately responded they don’t sell to individuals or sold it to individuals for a thousand euro per gram, others required a statement that I wouldn’t do anything illegal with the chemicals and a credit card number before cancelling my order. Eventually I found an address that was willing to order the chemicals for me, and a month later I had one gram of Nile Red delivered to my house.

I set up the required equipment, and looked at the paper that I planned to follow. I was missing methanol. As that was readily available on a big Dutch web shop, I mindlessly ordered it, not looking up the safety information about it. But when it arrived by normal mail and I opened it, being greeted by big warning labels and triple packaging, I realised the danger and immediately regretted that I ordered something dangerous trough mail. As I don’t have a fume hood and I’m not comfortable handling even slightly dangerous chemicals this project is for now on hold.

The UV flashlight did bring some interesting fun in the meanwhile, the subject of this post. Ever since visiting Idar Oberstein as a kid I have been fascinated with minerals and gems, and even found some while hiking and bought some others. While walking through my apartment looking at things under UV light, I took out the box with some of the minerals I had collected, and was surprised by the hidden beauty. After researching a bit more online, I found out more about different properties of elements when exposed to UV light;

1. Fluorescence

Fluorescence is the first property of substances you see when first using a UV light. The light in the UV spectrum is absorbed, and a colour in the visible spectrum is returned. You might have seen this at a party, where a white piece of clothing becomes fluorescent blue. But all kinds of interesting colours can be emitted. When the source of UV light is taken away, the re emitted light is also gone. Unlike Phosphorescence;

2. Phosphorescence

Phosphorescence is highly related to fluorescence, except that when the light source is taken away, it will still keep emitting visible light for a couple of minutes to a couple of hours. You may know these from the glow in the dark toys that were quite the rage when I was a child some 15 years ago, but this phenomenon also occurs in minerals!

3. Tenebrescence

Tenebrescence is a rare phenomenon where a mineral changes colour and changes back when not exposed anymore or exposed to a different wavelength. Some sunglasses are tenebrescent, but also some minerals can be! The best example I have of this is Hackmanite, which is dark purple initially, but becomes light grey when exposed to visible light, When left in the dark, it will recover it’s purple colour. Much cooler is to expose it to UV light, because the process is much faster, but also because after the orange glow disappears when removing the UV source, it is also phosphorescent emitting a fade green glow for a long time!

To share some excitement, I took some pictures in both visible and short wave UV to post here. Below each set of pictures the name of the mineral and the properties from above are listed.

Afghanite, Fluorescent
Calcite, Fluorescent
Cerrusite, Fluorescent
Fluorite, Fluorescent
Hackmanite, Fluorescent & Phosphorescent & Tenebrescent
Hauyn, Fluorescent
Kunzite, Fluorescent
Opal, Fluorescent
Ruby, Fluorescent
Selenite, Fluorescent
Sodalite, Fluorescent
Spinel, Fluorescent
Stilbite, Fluorescent & Phosphorescent
Tugtupite, Fluorescent

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