Amethyst is the purple variety of quartz, the same mineral as rock crystal and citrine. Its color comes from small amounts of iron in the crystal combined with natural radiation from surrounding rocks. It is hard enough for everyday jewelry, found on several continents, and has been the February birthstone on modern lists since 1912.
What amethyst is
Quartz is silicon dioxide, one of the most common minerals in the Earth's crust. Pure quartz is colorless. In amethyst, a few iron atoms sit in the crystal structure in place of silicon or in nearby gaps. On their own they do not make the stone purple. Over geological time, gamma radiation from traces of potassium, uranium and thorium in the host rock knocks electrons out of place and changes the charge on those iron atoms. The altered sites, called color centers, absorb yellow-green light and the crystal looks purple. You can read more about this mechanism on the color in gemstones page.
That origin explains two habits of the stone. Heat can undo the color center, so amethyst heated to a few hundred degrees Celsius turns yellow, orange or brown, which is how most commercial citrine is made. A few deposits produce green quartz (prasiolite) when heated. And because color centers grow along with the crystal, amethyst often shows color zoning: angular bands of deeper and paler purple that follow the crystal faces.
Amethyst has a Mohs hardness of 7, a refractive index of about 1.544 to 1.553 and a specific gravity close to 2.65. It shows weak to moderate dichroism, with two slightly different shades of purple when viewed through a dichroscope. Many natural crystals contain a pattern of fine twinning called Brazil-law twinning, which a gemologist can see under crossed polarizers.
Color grades and trade names
The finest amethyst is a deep, even reddish purple to purple with no brown or gray. Light stones are still pretty and much more plentiful. Traders use a few names you will see in listings:
- Siberian describes top color: deep purple with red and blue flashes. It originally meant stones from the Ural Mountains of Russia, but today it is a quality grade used for material from any source.
- Rose de France is pale lilac or lavender amethyst, popular in Victorian and Edwardian jewelry.
- Chevron amethyst is banded purple and white quartz, usually cut as beads or cabochons.
- Ametrine is quartz with purple and yellow zones in one crystal, covered on its own ametrine page.
Most faceted amethyst is eye-clean. Look for the typical inclusions under a loupe: fingerprint-like healed fractures, two-phase fluid inclusions and the striped "tiger stripe" pattern of color zoning. These help separate natural stones from synthetics.
Where amethyst comes from
Brazil and Uruguay
Southern Brazil (Rio Grande do Sul) and northern Uruguay (around Artigas) produce amethyst from geodes in ancient basalt lava flows. Gas bubbles in the cooling lava left hollow cavities. Silica-rich water later seeped in and lined them with quartz crystals, some purple. Split open, these geodes can stand taller than a person and are sold as decorative "cathedrals." Uruguayan material is known for deep, saturated color in smaller crystals. The process is part of how igneous rocks host gems.
Zambia and other African sources
Zambia's deposits, worked since the mid twentieth century, yield deep purple amethyst with a slightly bluish tone. Other African producers have included Namibia, Tanzania and Madagascar.
Russia, Mexico and the United States
The Ural Mountains gave the "Siberian" name its fame, and Russian amethyst filled Imperial jewelry in the eighteenth and nineteenth centuries. Mexico (Veracruz and Guerrero) produces pale to medium crystals with fine color zoning. In the United States, the Four Peaks area of Arizona is known for small, deeply colored stones.
Until the nineteenth century amethyst was rare enough to sit beside ruby and sapphire in price. The opening of large Brazilian deposits made it widely available, and it moved into the group the trade once called semi-precious.
Synthetic and treated amethyst
Synthetic amethyst grown by the hydrothermal method has been made commercially since the 1970s, with Russia a large producer. It has the same chemistry and properties as natural amethyst, so separating the two can take advanced testing at a lab. Clues include the absence of natural fluid inclusions, unusual color zoning and specific infrared spectra.
Natural amethyst is rarely treated to improve purple color, though some pale material may be heated lightly to remove smoky tones. Heating to produce yellow or green quartz is common and is covered in gemstone treatments explained. Glass and dyed quartz also imitate amethyst in low-cost jewelry.
Fading and care
Some amethyst can lose color if exposed to strong sunlight or heat for long periods. A ring worn every day will not fade quickly, but a stone kept in a sunny shop window or left on a dashboard can pale over months. Store amethyst away from direct sun and keep it away from jeweler's torches during repairs.
At Mohs 7, amethyst resists scratches from household dust, which is mostly quartz itself. It has no cleavage and breaks with a conchoidal fracture, so it is fairly tough. Clean it with warm soapy water and a soft brush. Ultrasonic cleaning is usually safe for untreated, inclusion-free stones, but avoid steam and sudden temperature changes. The jewelry cleaning guide covers the details.
Amethyst in history and folklore
The name comes from the ancient Greek amethystos, meaning "not intoxicated." Greeks and Romans carved drinking cups and wore amethyst in the belief that it guarded against drunkenness, perhaps because its wine-like color suggested watered wine. The story of a maiden named Amethyst turned to crystal by the goddess Diana and stained purple by Bacchus is much later; it comes from a poem by the French writer Remy Belleau published in 1576.
Amethyst also had religious meaning. It was set in the breastplate of the high priest described in the Book of Exodus, and Catholic bishops have long worn amethyst rings. In medieval Europe it was associated with piety and calm. These meanings are traditions, and the gemstone meanings and folklore page collects others like them.
In the modern birthstone list adopted by American jewelers in 1912, amethyst is the stone for February, a place it keeps on the current birthstones by month list. It is also a traditional gift for the sixth wedding anniversary.
Frequently asked questions
Is amethyst a precious stone?
Amethyst was once priced with ruby and sapphire, but large finds in Brazil made it common. Today it is a moderately priced gem, and fine deep-purple stones still command more than pale ones.
Does amethyst fade in sunlight?
Some amethyst can fade with long exposure to strong sunlight or heat. Normal wear does little harm, but avoid storing it in direct sun.
How can I tell natural amethyst from synthetic?
Natural stones often show fluid inclusions, angular color zones and Brazil-law twinning. Synthetic amethyst can be very clean, and a gem lab may be needed for a firm answer.
What is the difference between amethyst and citrine?
Both are quartz. Amethyst is purple from iron color centers, and citrine is yellow to orange. Heating amethyst destroys the purple color center and often turns it into citrine.