Amethyst Buying Guide
Gem lovers have long valued amethyst, the purple variety of quartz, for its deep color and clear crystal. Through the ages, amethysts have inspired spiritual symbolism in many societies. The February birthstone with the color of royalty, beautiful amethyst can showcase designs and fashions of all kinds, from simple to intricate. You’ll find it in many shapes and sizes.
Amethyst Buying and the Four Cs
The IGS amethyst value listing has price guidelines for faceted and cabbed gems.
With a hardness of 7 and lack of inclusions, amethyst makes a durable stone fit for any gem setting. Combining versatility and beauty, amethysts make excellent choices for jewelry or decorative pieces.
Amethyst receives its purple color from its iron content and natural irradiation under the Earth’s surface. Transparent gems are abundant. While high-quality amethysts aren’t difficult to find, exceptional specimens are still rare.
As with other colored gemstones, hue, tone, and saturation factors have the most impact on cost. A high-quality amethyst will show even color, without visible zoning. Amethysts range in color from light, pinkish purple stones to deep grape hues.
The most highly valued amethysts are “Siberian quality.” This term no longer refers to the stone’s origin. Rather, gemologists use it to refer to stones that exhibit red and blue flashes on deep purple color.
Consumers generally favor darker stones, ideally with 75-80% tone. Secondary blue hues, up to 20%, add depth to the gem. Secondary red hues may be present under incandescent light. Their presence indicates a truly exceptional amethyst.
Lighter stones have become popular for jewelry use. Gems with light lavender tones are marketed as “Rose de France” amethyst.
AAA to A Grades
After Siberian quality, amethysts may be graded from AAA down to A. Here, an AAA grading represents eye-clean stones with good color. An AA may have small inclusions or a weaker or darker color than AAA. A grade amethysts have light tones and inclusions. However, this scale isn’t standardized. Grades assigned to stones may differ somewhat between jewelers.
Since eye-clean material is so abundant, avoid included amethysts. Choose gems with high clarity grades. Amethyst crystals should show great transparency. Some specimens with small inclusions may be used for carving or cabochons. Small inclusions in large, dark stones may be tolerated. However, any inclusions in lighter stones will be more noticeable. Therefore, they will hold less value.
Because amethysts have such wide availability, poorly cut gems, even with good color, aren’t highly valued. Make sure your faceted stone has a symmetrical cut with correct proportions. Although you’ll commonly see amethysts with brilliant cuts, you can have them faceted in many different designs.
Recently, lapidaries have creatively cut mesmerizing patterns into some stones with good, even color.
Some rough specimens with well-formed crystals can be quite beautiful in jewelry as well.
Amethysts are available in all sizes, though large crystals of fine quality amethyst are rare. The largest specimens come from Brazilian mines. However, these tend to have color banding. Most consumers prefer the smaller but intensely colored stones found in Zambia. Price per carat climbs gradually. Above 25 carats, stones tend to decrease in value per carat.
Quartz crystals with both purple and yellow coloring – amethyst and citrine – are called ametrine. Currently found only in Bolivia, gem-quality ametrine tends to have moderate colors. The color zoning arises from slight differences in temperature and pressure during formation. Stones with high clarity are available in large sizes. Gem cutters generally cut them to flaunt their color transition.
Synthetic amethyst is common and serves as an inexpensive alternative to natural stones. Buyers beware of lab-grown stones sold as natural amethyst. You should only use jewelers who will certify the gem’s authenticity. For smaller stones, the cost of testing to distinguish between synthetic and natural could exceed the cost of the stone itself. Larger amethysts should be tested by an independent gemology laboratory. Be wary of amethysts too cheap for their size.
Although an uncommon practice, dark-toned amethysts may receive heat treatments to lighten them. This stable and permanent treatment requires no extra care.
Further heating can alter the stone’s color altogether, turning it into citrine or other quartz varieties with shades of green, red, brown, or colorless. Some vendors refer to amethysts turned green due to heating as “green amethyst.” This is a misnomer. While amethyst is the purple variety of quartz, the proper term for green quartz is prasiolite. A small amount of prasiolite occurs naturally. However, heat treatments create most of them. Heat-treated prasiolite may fade in sunlight. Store these stones away from the light.