Does Amethyst Fade in the Sun? Crystals That Lose Their Colour in Light

A-grade amethyst specimen

By Adam Kelliher

The short answer: yes, some amethyst can fade with long exposure to strong light, and heat can change its colour for good. Kunzite, some topaz and a few other stones are also known to fade, so keep them out of a sunny window.[1][2]

We get this question a lot from people who keep a geode on a sunny windowsill. Here's what's going on, and what to do about it.

Why amethyst is purple

Amethyst is quartz. Its purple comes from a tiny amount of iron in the crystal, on the order of a few hundredths of a percent, which natural radiation turns into a purple colour centre.[2] That colour is stable in normal room light, but it isn't permanent under every condition.

Light

GIA says some amethyst colour can fade with prolonged exposure to intense light.[1] Note the words "some" and "prolonged". A day in the sun won't bleach your geode, but years in a south-facing window can lighten it. Not every amethyst fades at the same rate, and you can't tell in advance which will.

Heat

Heat is the bigger risk. Heating amethyst changes those colour centres and turns the purple yellow or orange. GIA notes that natural citrine is rare and most citrine on the market is heated amethyst.[3] GIA also warns that sudden temperature changes can fracture amethyst, so keep it away from heaters, steam cleaners and hot car dashboards.[1]

Americruz amethyst from Skamania County, Washington
Americruz amethyst from Washington State. (photo: Rubble Rock & Gem)

Other stones that fade in light

  • Kunzite. GIA notes its colour can fade with prolonged heat or intense light, whether the colour is natural or treated.[4]
  • Topaz. GIA lists topaz alongside amethyst and kunzite as gems that light and heat can fade.[5]
  • Amber goes the other way. It tends to darken with too much light.[5]

For a deeper list of colours that change under UV, read Vanishing Hues. Some stones have the opposite problem with water, which we cover in Water-Sensitive Stones.

How to display it

  • Keep amethyst out of direct sun. A shelf across the room from the window is fine.
  • Use LED lighting in display cases. LEDs run cool, so they don't add heat.
  • Clean it with warm soapy water, not steam.[1]
  • If you have a big geode near a window, turn it now and then and compare the sides. That's a cheap early warning.
Amethyst cathedral geode
An amethyst cathedral. Big pieces like this belong away from a sunny window. (photo: Rubble Rock & Gem)

Browse our crystals, and look at displays for stands and cases that keep pieces out of harm's way.

See what's new: browse our newest arrivals for the latest pieces added to the shop.

Sources

  1. GIA (Gemological Institute of America), Amethyst Care and Cleaning Guide.
  2. GIA, Gems & Gemology: Russian Synthetic Ametrine (how iron and ionizing radiation create amethyst colour).
  3. GIA, Citrine buyer's guide and FAQ: Is citrine treated?
  4. GIA, Kunzite Care and Cleaning.
  5. GIA, Tips on Caring for Jewelry: Be Careful with Light and Heat.

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