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Natural Fluorescent Hackmanite Sphere 65mm
€70.00 EUR
Tenebrescent Gemstones
Tenebrescence is a reversible color change caused by light: the stone takes on color or darkens under ultraviolet light, then slowly fades back in ordinary daylight, and the cycle can be repeated again and again. The best known tenebrescent mineral is hackmanite, a sulfur-bearing variety of sodalite (Na8Al6Si6O24(Cl,S)2), which turns pink to purple after a short time under a UV lamp or in strong sunlight.
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Gemstone guide
Tenebrescent Gemstones
About tenebrescence
The word comes from the Latin tenebrae, darkness. Hackmanite is named after the Finnish geologist Victor Hackman. The color comes from color centers linked to sulfur in the crystal structure: ultraviolet light activates them, and visible light returns them to their resting state, without any lasting change to the stone. Hackmanite is found in Afghanistan, Myanmar, Canada, Greenland and Russia, among other places, and a few other minerals, such as tugtupite, show the same effect.
What you'll find in this collection
Hackmanite in two forms: rough pieces from a few grams to around 20 grams, white, lavender or pale pink in daylight, and polished spheres of 58 to 65mm. All of them turn purple after UV exposure and glow a strong orange under a 365nm UV flashlight, so they suit fluorescent mineral collections as well.
How to recognise tenebrescence
Shine a UV lamp on the stone for a minute or two, or leave it in strong sunlight: the color deepens to pink or purple. Under white light it fades again, within minutes to several hours depending on the piece. Under longwave UV (365nm) hackmanite also fluoresces a strong orange, a separate effect that shows only while the lamp is on.
Caring for hackmanite
With a hardness of 5.5 to 6, hackmanite is softer than quartz, so store it apart from harder stones. Clean it with lukewarm water and a soft cloth, and avoid ultrasonic cleaners and harsh chemicals. The color fading in daylight is normal and does no harm: a few minutes under UV brings it back.
Every stone is natural, and each listing gives its weight, size, origin and treatment, with photos of the actual stone.