The world's most popular purple gem. Birthstone for February.
Author: Hobart M. King, PhD, GIA Graduate Gemologist
What is Amethyst?
Amethyst is the world's most popular purple gem. It is the purple color variety of quartz that has been used in personal adornment for over 2000 years.
Amethyst is the birthstone of February and an important New Age gem. It is used to produce faceted stones, cabochons, beads, tumbled stones, and many other items for jewelry and ornamental use.
Amethyst has a Mohs hardness of 7 and does not break by cleavage. That makes it durable enough for use in rings, bracelets, earrings, pendants, and any type of jewelry. Enormous deposits of amethyst in South America and Africa provide enough amethyst to keep the price low. Most people can easily afford amethyst.
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Color in Amethyst
Amethyst is an extremely popular gem because of its attractive purple color. Like the word "turquoise," the word "amethyst" is now the name of a color as well as the name of a gem material.
While the word "amethyst" makes most people think of a dark purple gem, amethyst actually occurs in many purple colors. The purple color can be so light that it is barely perceptible or so dark that it is nearly opaque. It can be reddish purple, purple, or violetish purple. Amethyst exists in this wide range of colors.
Today much of the light amethyst is used to cut small calibrated stones for use in mass-market jewelry. Most of the premium reddish purple color amethyst is being used in high-end or designer jewelry.
Creative people have come up with a variety of adjectives to describe shades of amethyst. These include: orchid and lavender for lighter colors; grape, indigo or royal for darker colors; and raspberry or plum for reddish colors. While these names can be useful in conveying a generalized color, they are by no means precise or clearly understood by everyone.
With a combination of attractive colors, good durability, and affordability, it is no wonder that amethyst is a favorite gem of artisans, jewelers, craftspeople, and consumers.
The first step in amethyst receiving its purple color begins during crystal growth. That is when trace amounts of iron are incorporated into a growing quartz crystal. After crystallization, gamma rays, emitted by radioactive materials within the host rock, irradiate the iron to produce the purple color.
The intensity of amethyst's purple color can vary from one part of the crystal to another. These color variations, known as “color zoning,” are caused by varying amounts of iron being incorporated into the crystal during different stages of crystal growth.
Amethyst crystals grow slowly and the composition of the fluids delivering the iron and the silica needed for crystal growth can vary. The darkest color of amethyst forms when the largest amount of iron is incorporated into the growing crystal. That is what causes color zoning.
Color zoning influences the marketability and value of amethyst. Most people want a gem with a rich and uniform color. As a result, gems of uniform color - no color zoning - are the most desirable and the most valuable.
Physical Properties of Amethyst
The physical properties of amethyst are almost identical to the physical properties of other color varieties of quartz. The only important difference is the color of the material.
Physical Properties of Amethyst
|Color||By definition, amethyst is purple in color, the most popular color is a reddish purple with rich saturation.|
|Streak||Colorless (harder than the streak plate)|
|Diaphaneity||Transparent to translucent|
|Cleavage||None - typically breaks with a conchoidal fracture|
|Specific Gravity||2.6 to 2.7|
|Diagnostic Properties||Conchoidal fracture, glassy luster, hardness, purple color|
|Uses||Faceted stones, cabochons, beads, tumbled stones, ornamental objects.|
Geologic Occurrence of Amethyst
Small amounts of amethyst are found at many locations throughout the world in igneous, metamorphic, and sedimentary rocks. Faceting, cabbing and ornamental grade amethyst can be found in all of these locations; however, the amount is usually insufficient to support an ongoing mining operation.
The world’s most important amethyst deposits are usually found in the fractures and cavities of igneous rocks. In Brazil and Uruguay large amounts of amethyst are found in the cavities of basalt flows. Large cavities can contain hundreds of pounds to several tons of amethyst crystals.
Smaller cavities, known as geodes, are often opened in a way that displays the crystals inside and then fitted with a base that allows them to be used as home or office decor. They are popular sales items at rock shops and mineral shows.
Other productive amethyst deposits are located in Canada, France, India, Madagascar, Mexico, Morocco, Myanmar, Namibia, Russia, South Africa, Sri Lanka, Tanzania, and the United States.
Amethyst has been produced at many locations in the United States. Much of it has been as a byproduct of other mining operations. Today, the only commercially run amethyst mine in the United States is the Four Peaks Mine in Arizona. The mine is well known for producing amethyst with a reddish purple color. The deposit was also known by Native Americans because a few amethyst arrowheads have been found nearby. Some of the amethyst in the Spanish crown jewels may be from this deposit, brought back to Spain by Spanish explorers. 
Amethyst by the Ton
Amethyst is best known as a purple, transparent, faceted gem that is sold by the carat. However, most of the world’s amethyst production is commercial products that are sold by the pound, kilogram or ton. These include amethyst geodes, amethyst crystal plates, amethyst crystals and amethyst tumbled stones.
The amethyst geode market is very strong, with many tons of them being sold at the Tucson Gem and Mineral Show alone. Small amethyst geodes are one of the most ubiquitous geological items offered for sale. They can be found at gem shows, rock shops, metaphysical stores, and novelty shops around the world.
World Amethyst Production
|The United States Geological Survey estimated the world’s commercial amethyst production between 2006 and 2016. Much of this production is sold in the form of geodes, crystal plates, crystals, and tumbled stones. An amazing amount of amethyst is being produced. Data from the United States Geological Survey. |
The geodes can be small enough to hold in the palm of your hand, or enormous sections of lava tubes that can be several meters long and weigh several tons. People buy them for home decor, mineral collections, and metaphysical use or just because they like them.
The United States Geological Survey has estimated the world’s commercial amethyst production between 2006 and 2016. Bolivia, Brazil, Tanzania, Uruguay and Zambia were the countries with the highest production. Statistics on their production are shown in the accompanying table.
"Grape Agate" or Botryoidal Amethyst
In 2016, mineral dealers began selling specimens of "grape agate". The specimens were composed of tiny purple spheres that ranged in size between about 2 and 8 millimeters across (see accompanying photo). The specimens were called "grape agate" because of their purple color, their botryoidal habit (from the Greek botrys, meaning a "bunch of grapes"), and because of their translucent appearance. "Grape agate" quickly became a popular new mineral specimen because of its wonderful color, fun name, and interesting appearance.
However, a few people questioned the identity of the material, doubting that agate was the proper name. When it was noticed that the grapes had a drusy surface (drusy means "covered with crystals"), the identity of "agate" was realized to be incorrect. Why? Because agate, as a variety of chalcedony, has a microcrystalline texture, while common quartz has a crystal size that can be recognized with the unaided eye or with only a low level of magnification.
Although specimens of this material are still called "grape agate", a more appropriate name is "botryoidal amethyst". In the gem and mineral trade, incorrect names such as "grape agate" are called "misnomers".
One of the world’s most interesting gem materials is ametrine. It is a variety of bicolor quartz in which citrine and amethyst occur in contact with one another in a single crystal. The word AMEthyst and ciTRINE were combined to yield the name “ametrine.” This gem material is rarely found in nature, and the only commercial production is from the Anahi Mine in eastern Bolivia. There the bicolor quartz crystals have formed within the fractures and vugs of a dolomitic limestone of the Murcielago Group. 
Amethyst Treatment to Citrine and Prasiolite
The color of amethyst can often be modified by heating. Much of the yellow to golden quartz sold as “citrine” is actually amethyst that has been modified by heating. This heating can be natural or done intentionally by people.
Natural or intentional heating can also change the color of amethyst to a pale green. The proper name for this material is prasiolite; however, many sellers call it “green amethyst.” These sellers run the risk of legal action from their customers or the Federal Trade Commission, who say that “it is unfair or deceptive to describe a product with an incorrect varietal name.” In fact, the Federal Trade Commission has used “green amethyst” and “yellow emerald” as examples of potentially misleading names. 
Some prasiolite is also produced by irradiation of natural amethyst. This produces prasiolite with a lighter green color. This color can be lost if the material is heated to temperatures over 150 degrees Celsius.
Heating is also used to lighten the color of extremely dark amethyst or eliminate a brown tint that can be seen in many natural materials.
Care of Amethyst Gems and Jewelry
Amethyst is a durable gemstone, but some care is needed to maintain its polish and natural color. Amethyst has a Mohs hardness of 7, and that is generally considered hard enough for almost any jewelry use.
However, with a hardness of 7, it can come in contact with a variety of common objects that can produce a scratch on its surface. Accidental scrapes on hard objects or abrasion with other gems of equal or greater hardness in a jewelry box can cause damage. Amethyst is also a brittle material that can be chipped or scratched by impact. It is best not to wear amethyst jewelry during an activity or at a location where this might occur.
Long-term storage of amethyst and amethyst jewelry is best done in a jewelry box or other dark location. The color of some amethyst can be subject to fading by prolonged exposure to direct sunlight or bright display lights.
Even though amethyst is not an extremely costly material, synthetic amethyst has been manufactured at least as far back as 1970. Since then an enormous number of items have been produced from synthetic amethyst by faceting, cabbing and carving. These have entered all levels of the jewelry trade. This has disappointed many jewelry consumers and made them hesitant to purchase amethyst.
Experienced gemologists can identify some natural amethyst with a microscope if it exhibits color zoning and contains characteristic mineral inclusions. However, much of the natural amethyst is of a very high clarity grade, and finding identifying inclusions can be difficult or impossible.
In the early days of synthetic amethyst, most synthetic material did not exhibit Brazil law twinning, which is almost always present in natural amethyst. This could be used to identify some synthetic material, but when synthetic amethyst manufacturers learned of this, they began using twinned amethyst slices as seed crystals. Now almost all synthetic amethyst is coming out of the lab with Brazil law twinning.
Purple is a popular gemstone color and although natural amethyst is relatively inexpensive, some simulant materials are used. Purple glass is the most common and least expensive. Purple synthetic corundum is a more durable and convincing simulant.
Another amethyst simulant is Nanosital, a man-made glass-ceramic that is manufactured in Russia in a variety of gemstone look-alike colors. One of these is a rich purple material that is sold as an amethyst simulant. It can easily be separated from natural amethyst with a polariscope. To do that, cross the polarizing filters, place the stone on the lower polarizing filter, then rotate the stone. Natural amethyst will produce an obvious blink while Nanosital will remain dark in any orientation.
 About the Four Peaks Amethyst Mine: Article on the FourPeaksMining.com website, accessed February 2017.
 Ametrine: an article on the Geology.com website, accessed February 2017.
 Guides for the Jewelry, Precious Metals, and Pewter Industries, proposed revisions; Federal Trade Commission; 16 CFR Part 23, 2015. Link to excerpt.
 A Simple Procedure to Separate Natural from Synthetic Amethyst on the Basis of Twinning: by Robert Crowningshield, Cornelius Hurlbut, and C. W. Fryer, Gems & Gemology, Fall 1986, pages 130-139.
 Trends in World Colored Gemstone Production, 2006 - 2016: by Thomas Yager, Gems & Gemology, Fall 2018, pages 324-325.
Amethyst as a Healing Stone?
People have collected gem materials for thousands of years and marveled over their beauty. Through time and in all parts of the world, many people have believed that gem materials have the ability to heal, protect, or comfort a person who owns or wears them.
Even though there is no scientific evidence that gemstones have any healing or spiritual power, many people persist in these beliefs. Today, amethyst is one of the most popular "healing stones." Millions of dollars per year are spent on amethyst crystals, tumbled stones, beads and other amethyst items for use in these practices.
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