What Causes the Color of Amethyst
Amethyst is a variety of quartz that is known for its beautiful purple color. The color of amethyst ranges from a light lilac or lavender to a deep, intense royal purple, and from brownish to vivid. It can also be a combination of these colors, creating a mesmerizing and unique gemstone. Amethyst's purple color is due to the presence of trace amounts of iron in the quartz crystal structure. The more iron that is present, the deeper the purple color of the amethyst.
The purple color in ghost town glass comes from small amounts of manganese in the glass when it has been exposed to ultraviolet light. The manganese was used as a clarifying ingredient in glass from 1860 to 1915. Prior to that, lead was used, and subsequently, selenium is used.
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| What Causes the Color of Amethyst? |
Quartz will commonly contain trace amounts of iron ( in the range of 10's to 100's parts per million of iron). Some of this iron sits in sites normally occupied by silicon and some is interstitial ( in sites where there is normally not an atom). The iron is usually in the 3+ valence state.
Gamma ray radiation ( from nuclear decay in the surrounding rocks ) can knock an electron from an iron lattice site and deposit the electron in an interstitial iron. This 4+ iron absorbs certain wavelengths (357 and 545 nanometers) of light causing the amethyst color. You need to have quartz that contains the right amounts of iron and then is subjected to enough natural radiation to cause the color centers to form.
The color of amethyst has been demonstrated to result from substitution by irradiation of trivalent iron (Fe3+ ) for silicon in the structure, in the presence of trace elements of large ionic radius, and, to a certain extent, the amethyst color can naturally result from displacement of transition elements even if the iron concentration is low.
Amethyst occurs in primary hues from a light pinkish violet to a deep purple. Amethyst may exhibit one or both secondary hues, red and blue. The best varieties of amethyst can be found in Siberia, Sri Lanka, Brazil and the far East. The ideal grade is called "Deep Siberian" and has a primary purple hue of around 75–80%, with 15–20% blue and (depending on the light source) red secondary hues.
Amethyst Losing Its Color
Amethyst can fade in tone if overexposed to light sources, and can be artificially darkened with adequate irradiation.
Amethyst crystals can lose their color due to exposure to heat and radiation.
Heat: When amethyst is heated to between 300 and 500 degrees Celsius, its purple color fades and it may turn yellow, orange, brown, or even colorless. The exact color change depends on the temperature and the duration of heating.
Radiation: Exposure to high levels of radiation, such as from ultraviolet light or X-rays, can also cause amethyst to lose its color. This is why it is important to store amethyst jewelry and other amethyst crystal items in a cool, dark place.
Tips for preventing your amethyst crystals from losing their color:
- Store your amethyst crystals in a cool, dark place.
- Avoid exposing your amethyst crystals to direct sunlight or other sources of ultraviolet light.
- Avoid heating your amethyst crystals.
- Be careful when cleaning your amethyst crystals, as some cleaning products can damage the color.