#tenebrescence

Scientists Say: Tenebrescence

It’s rare, but some minerals display this color-warping property

Tenebrescence is a property of some minerals that change color under certain lights, such as ultraviolet (UV) or bright sunlight. These color shifts last even after light exposure ends. The minerals do eventually fade back to their original color. But that takes time. Some fade in a matter of seconds. Others take hours or more. This slow fade sets tenebrescence apart from fluorescence. That’s another light-related mineral property. Fluorescent minerals also color shift. But the effect ends when the light exposure does.

Photochromic Sodalite aka Hackmanite Specimen Tenebrescent (Photochromism) & Fluorescent - Color Changes to Deep Purple! $20 plus shipping.

https://www.oldearthminerals.com/shop/p/7no60a017hl2jl4hall48i5hnmjbgj-sb6hb-w95xb-j9n8f-pg5nx-dlkzb-8jy4k-3xhxm

Sodalite var. Hackmanite with Richterite displaying fluorescence and tenebrescence

Locality: Koksha Valley, Badakhschan Province, Afghanistan

Hackmanite: The chameleon mineral.

A pink to purple variety of the mineral Sodalite (see http://on.fb.me/1IakMRj), it displays the weird property known as tenebrescence (aka reversible photochromism), a change of colour in response to sunlight or UV. Material from Quebec and Greenland starts off purple when wrested from the Earth, and fades to a greyish colour, while Burmese or Afghan material develops a strong violet to pink colour when exposed to sunlight that fades when the stone is left in the dark. The effect can be repeated at will (and is exploited in self darkening glasses), but heating the stone destroys it. The energy of the light creates or alters electronic colour centres in the crystal that selectively absorb wavelengths, leaving behind a residual colour such as the red of rubies. In this case it is the electrons of sulphur disseminated in the crystal structure that produce this eerie colour change capacity. Some people call it giving the stone a suntan, if you let Asian Hackmanite fade in the dark and then shine a UV light on it or open the curtain, a near instant colour change results (while it takes a week in the dark for the hue to fade again), a game which is an occasional staple of mineralogy demonstrations.

Before 1991 only small crystals were known, and cuttable material now comes from Canada, Afghanistan and Burma. The variety was named after a Finnish geologist after its discovery in Greenland in 1896. With a Mohs hardness of 5.5-6, it is just about suitable for jewellery use. the specimen is from the Lapis mines of Badakhshan (see http://on.fb.me/1KmBzjI),.

Loz

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Color Changing (Tenebrescent / Photochromic) Sodalite var Hackmanite Crystal from Badakhshan, Afghanistan. This color change is temporary and will go back to the original color when kept out of UV light.

https://www.oldearthminerals.com/shop/p/7no60a017hl2jl4hall48i5hnmjbgj-sb6hb-w95xb-j9n8f-pg5nx-dlkzb