Learn the Magical Reason Why Some Minerals Transform Color

By Jessica Stewart on March 3, 2020

 

Did you know that, just like a mood ring, some minerals can change color? Instead of being affected by temperature, however, these minerals magically transform when exposed to light. The phenomenon, known as tenebrescence, might be more familiar to people when they think of light-adaptive sunglasses. Just as these lenses lighten and darken according to the type of light they’re exposed to, tenebrescent minerals change color in the same way.


 

 

광물은 어떻게 해서 카멜레온처럼 색을 바꿀까


   여러분은 무드 링처럼, 몇몇 광물들이 색을 바꿀 수 있다는 것을 알고 있나? 그러나 이러한 광물들은 온도의 영향을 받는 대신 빛에 노출되면 마법처럼 변한다. 발광으로 알려진 이 현상은 사람들이 빛에 적응하는 선글라스를 생각할 때 더 이해가 쉽다. 이 렌즈들이 노출되는 빛의 종류에 따라 가벼워지고 어두워지는 것처럼, 네발 초승달 광물도 같은 방식으로 색을 바꾼다.




광크롬으로 알려진 이 변형능력은 1896년 그린란드에서 처음 발견되었다. 지질학자들은 처음 분리되었을 때 몇몇 종류의 소달라이트가 밝은 분홍색이라는 것을 우연히 발견했다. 밝은 빛에 그대로 노출되어 있기 때문에 소달라이트에서 서서히 색이 바래고, 다만 자외선에 노출되었을 때 분홍빛 빛깔을 되찾을 뿐이다. 이러한 광물에서는 열을 가하지 않는 한 변형이 무한하며, 장파 또는 단파 UV 광선의 사용으로 가속된다.


그렇다면 어떤 광물이 이와 같은 특별한 "초능력"을 가지고 있을까? 해크마나이트는 다양한 소달라이트로 가장 많이 인용되는 4대 초승달 광물 중 하나이다. 퀘벡과 그린란드에서 발견되는 다양한 색들은 밝은 빛으로 남겨지면 짙은 보라색/핑크색에서 초록색-흰색으로 변한다. 그러나 아프가니스탄과 버마에서 채석한 해커들은 햇빛에 노출되면 흰색으로 시작하고 분홍색으로 변한다.


허그마나이트는 변형하기 가장 쉬운 광물 중 하나일 수도 있지만, 4대 초승달인 다른 몇몇 광물들도 있다. 여기에는 고에너지 방사선에 노출되면 어두워지는 스포두민(spodumene)과 약간의 연한 색상의 예인성 품종이 포함된다. 줄다리기에서는 단파 UV 광선이나 강한 햇빛에 노출되면 연분홍색 품종이 색의 강도를 얻는다.


황기철 콘페이퍼 에디터 큐레이터

Ki Chul Hwang, conpaper editor, curator


edited by kcontents


Also known as reversible photochromism, this transformative ability was first discovered in Greenland in 1896. Geologists happened upon the discovery when they noticed that some types of sodalite are bright pink when first broken off. The color slowly bleaches out of the sodalite as it remains exposed to bright light, only to regain the pink hue when exposed to UV light. In these minerals, the transformation is indefinite, unless they’re heated, and it’s accelerated by the use of either longwave or shortwave UV light.


 



So which minerals have a special “superpower” like this? Hackmanite, which is a variety of sodalite, is one of the most commonly cited tenebrescent minerals. Varieties found in Quebec and Greenland move from a deep violet/pink to a greenish-white color when left in bright light. However, hackmanite quarried in Afghanistan and Burma starts off white and gains a pink color when exposed to sunlight.


While hackmanite might be one of the easiest minerals to transform, there are several others that are also tenebrescent. These include spodumene, which darkens when exposed to high-energy radiation, and some light-colored varieties of tugtupite. In tugtupite, pale pink varieties gain an intensity of color when exposed to shortwave UV light or strong sunlight.


In case that wasn’t cool enough, there are many minerals that are capable of different visual and color transformations. In fact, tenebrescence is often confused with fluorescence, which is the ability for some minerals to emit light when they’ve absorbed light or radiation. It is actually much more common than tenebrescence—15% of minerals are able to fluoresce. While some minerals fluoresce in their pure form, most show this ability when they contain impurities called activators. Activators can include magnesium, lead, copper, and titanium.


No matter what the cause may be, fluorescence is one of the most thrilling parts of collecting minerals. This property is often used to find minerals out in the field, with hobbyists and geologists using UV lights to make them stand out to the naked eye. Once in hand, fluorescence can be manipulated to great effect. A geology enthusiast known as wild_nrocks on Instagram often shows off rare minerals he finds in northern Russia by letting them shine. From a rough piece of sodalite that looks like glowing lava to smoothed out eggs that emanate in the dark, these minerals are a thrilling sight to be seen.




Some minerals change color when exposed to light, an effect known as tenebrescence.






While others have a luminescent glow due to fluorescence.

 


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