Throughout history, amethyst has been engraved, sculpted, faceted, tumbled, and even eaten! (Not recommending that, though.) Once associated with royalty, this purple wonder was considered a high value gem due to its purity and beautiful color, even having, at one time, the same value as ruby and sapphire. Traces of its use in jewelry date back as early as 3000 BCE in ancient Egypt.

The Gemstone

Amethyst is the purple/violet variety of the quartz family. Its color ranges from pale lilac (called Rose de France in the market) to a deep saturated purple. It’s a 7 on the MOH’s hardness scale and is considered a gem with good tenacity and durability in general.

Its name comes from the Greek word amethystos meaning not drunken. The humorous name originates from what people believed to be one of its powers, i.e. that the stone could ward off intoxication! Interestingly, Greek legends associated amethyst with Dionysus, the god of wine and pleasure.

Its crystalline structure is rhombohedral, generally an elongated asymmetrical prism with twin pyramids on each side if unbroken in the rough. It can also be seen as a hexagonal prism or with hexagonal angular color zonings.

Amethyst is a gemstone with pleochroism, meaning that, depending on the viewing angle, the gem can display different hues/colors. In displaying two colors (dichroic), one hue can be more reddish, while the other can be more bluish.

The gem owes its stunning purple/violet-ish hues to trace amounts of iron and natural radiation within the Earth. Most of the citrines and prasiolites sold today are, in fact, heated amethyst. Whether this heating is natural or caused by man, the difference is generally indistinguishable. It doesn’t take a very high temperature, only about 470-750o Celsius is needed to change its color. And, if so desired, it can then get its purple color back with irradiation.

Ametrine a gemstone that is half citrine (yellow) and half amethyst (purple) and is the result of natural heating. Its color may fade over time with prolonged exposure to light and heat, causing it to be not as stable as we might think.

Amethyst can be found in large sizes and in plentiful quantities in many countries, namely, Brazil, Uruguay, Canada, Morocco, India, Mexico, Namibia, Siberia, Russia, and Sri Lanka. In Canada, the gem is sourced mainly in Thunder Bay, Ontario, but can be found in smaller quantities all over Canada.

The most desired qualities today are those gems with deep saturated purples in different hues. Siberian amethysts imbued with a deep purple color, with red and blue flashes, were among the most prized and expensive varieties. Alas, the Siberian stock ran out decades ago, making these gems so rare that the only ones to surface are from old stock.

A relatively new source of amethysts that showed up a few years ago in Tucson is Morocco. These gems have red hair-like inclusions of hematite, and hourglass-shaped color zonings. Moroccan amethysts are considered a breath of fresh air for those who want something a little more out of the ordinary for their birthstones.

Depending on its origins (Africa or Uruguay, for example) amethyst can have slightly different hues, i.e. a more purplish color or a more violet-ish color.

Imitations, Synthetics, and Confusion

Even though it’s considered a very affordable gem-stone in the jewelry market, amethyst has many impersonators. Glass and plastic are the most well-known. Some confusion also occurs with natural gemstones such as faceted purple fluorite, scapolite, spinel, sapphire, tanzanite, and iolite, to name just a few.

Lab-grown (synthetic) amethyst quartz is also widely used and is hard to differentiate from natural amethyst.

Synthetic quartz is used not only in jewelry but is an important part of everyday life. It is used to make lenses, prisms, timekeepers, UV windows, semiconductors, medical devices, tools for harnessing solar energy and detecting radiation, and in myriad aspects of scientific and aerospace research due to its piezoelectric properties.

While it might not be the bright amethyst we see in jewelry, it’s still impressive to see what can be done with quartz in general, not only the purple variety.

Differentiating synthetic amethyst from natural amethyst when it is cut (faceted or cabochon) is a complicated and costly task. Therefore, it is important to trust the supplier and their sources.

If the stone has a few inclusions, it may become easier for gemologists to differentiate it under the microscope. Otherwise, it’s almost impossible to discern. Inclusions are like a fingerprint.

Treatments and Care

There are few treatments used on amethyst since it’s an inexpensive gemstone, although, as stated above, it can be heated, irradiated, and dyed (rarely) to change its color.

Under artificial light, amethyst can appear darker than reality. Prolonged exposure to heat can also alter the color of the stone, so it’s unwise to solder or repair a piece of jewelry with the amethyst still set in it.

GIA suggests avoiding thermal shocks, as it can fracture and stress the gem. But ultrasonic and steamer procedures are generally safe, if we avoid high heat and then ice water right after. Important historical pieces are worth repairing with a lapidary artist, but smaller ones are often not worth the cost of repair.

February’s Birthstone

Not only is amethyst the birthstone for February, but it is also the gem of choice for the sixth wedding anniversary! It was officially added as February’s birthstone in 1912, when the American National Retail Jewelers Association (now known as Jewelers of America) created a standardized list of birthstones.

Before 1912, the assignment of gemstones to specific months varied widely by culture and region. Amethyst became the official choice for February likely due to its prominence and appreciation in history.

Amethyst jewelry is a popular gift for babies born in February as well as for women of any age to celebrate their birthdays.

Mining Amethyst

Brazil is the world’s leading source of mined amethyst and amethyst geodes. Some of the most significant deposits were found in Marabá and Pau d’Arco at the end of the 19th century.

Today, Minas Gerais is an important source of amethyst geodes, but the biggest production of the purple gem is in the state of Rio Grande do Sul in southern Brazil. This area is especially known for both its gem-quality crystals and decorative geodes.

Each of these areas represents a distinct geological setting, which results in different mining techniques being used. A large portion of the amethyst from these areas is heat-treated to produce citrine.

Buyers typically purchase amethyst directly from tunnel owners and then cob the material—in other words, they remove unwanted matrix and damaged portions—either at the mining site or at another location to prepare the gem as rough.

In Rio Grande do Sul, the amethyst occurs in vugs or geodes, which are cavities lined with mineral crystals within basalt. Sometimes the amethyst completely fills the cavity; other times it simply lines the inner surface.

This helps the mine owners and dealers decide whether to keep their discovery as a geode specimen or whether to remove the crystals for cutting for the jewelry market. The crystal quality, color and shape also play a role in their decision.

Purple Glory

With its rich history, amethyst continues to captivate the jewelry world even after centuries of admiration. From its origins as a gem of royalty and spiritual significance to its modern role as a February birthstone, this quartz variety remains timeless. Its accessibility, durability, and unique qualities ensure that amethyst retains a special place in the hearts of gem enthusiasts, gemologists, and artisans alike.

Its ongoing appeal demonstrates that even in a world of ever-changing trends, classic gemstones like amethyst can still surprise and inspire. For those who seek elegance, history, and a touch of mysticism in their jewelry, amethyst remains a gemstone with a regal allure.

The post Amethyst’s Regal Allure appeared first on Incolor Magazine.

In past issues, InColor has delved into the world of lapidary artists, illuminating the intricate processes of cutting, polishing and engraving gemstones. In this article, we take a more detailed look at the relationship of the successful gemstone cut in terms of depth and critical angle.

As most people know, gemstone cutting is not only an art form; it is also a scientific study. Having a badly cut stone can have multiple consequences, especially in the pavilion area resulting in fisheye, dead zones, an asymmetrical look, windows, etc. When dealers put a price on a gemstone, all these factors are taken into account. It’s important, therefore, for cutters to understand the critical angle in a gemstone.

What is critical angle?

The critical angle is, well, critical for a good cut! In a sense, it’s the shallowest angle you can cut a gemstone with, so that the light can be reflected back. That’s right, a gemstone doesn’t shine, it reflects. (Take that, Rihanna!)

If you go under the critical angle when cutting, you will get a window in the stone and the stone will lose color at its center without any facets to reflect the light back. If you play a bit and add a few degrees to the angle while cutting the stone, then you can get the perfect refraction inside, and the best reflection of the light as the gemstone will show good color back from all angles, and not show dead zones or windows.

But if you add too many degrees to your critical angle, there is a risk of causing dead zones in the gem, i.e. dark spots where no light gets reflected back. This is also why it is important to know the refractive index (RI) of the stones. The RI describes the optical density of a gem, i.e. when light enters a gemstone, it is refracted (bent) depending on the density of the material, and that refraction is measured. The RI can be found easily for most gems. In faceting, it basically indicates the usable angles you can cut into the stone so that it sparkles.

For those interested in calculating the critical angle,= below is a simple formula:

Sin-1 (1/N)
N= RI (Refractive Index)

Using the critical angle was perfected in the diamond cutting industry, and is also why all the round brilliant cut diamonds with the same diameter and quality will have similar depths.

The colored gemstone world has not yet made it a standard, and commercial quality gemstones often show poor cutting, but professional cutters try their best to cut their gems with the perfect angles.

Why is my stone so shallow/deep?

I’ve often had clients ask me why this or that gem was so shallow, while another was so deep? Why don’t all gemstones have the same calibrated depth? Why would two emeralds of the same diameter have different depth and pavilions? There are a few reasons:

1. Choice of the cutter or the customer
2. Retention of rough weight, or not enough rough
3. Critical angle variations
4. Dependent on the jewelry design
5. Repair work
6. Optical phenomenon and color

Choice of the Cutter or the Customer

Cutters can decide on any design they wish for their stones. Aesthetics can sometimes win over the retention of weight, as does the desire to test a certain type of cut even if the rough called for another shape. As an example, we can cut a “bluff stone,” a gem with a bigger diameter but shallow and light, instead of multiple smaller stones, with normal depth.

Or we can take the portrait cut as an example, where we want the biggest window possible for the stone. If the stone is opaque, there is no specific angle to follow since no light is reflected inside the stone. On these occasions, the customer or the cutter will decide what to do with the stone.

Retention of rough, or not enough rough

Sometimes, the only intent behind a cut is to lose aslittle rough as possible. In these cases, critical angle can rarely be achieved. The best scenario is to cut the biggest stone possible, as deep as possible, so that it can sell more for the weight than the stone itself is worth. This often happens for medium to lower quality corundum, where stones sell at a lower price per carat. The result is a fatter stone that costs more.
What can also happen is that you have a rough stone that is on the thin side, and there is no choice but cutting a gem with a window in it in order to be able to sell it at a desired price point. In the end, the cutter must decide if he/she wants to try faceting a larger stone with less than perfect proportions, or a smaller one with perfect proportions. It will depend on the price of the rough, and the price for the finished gem.

Critical Angle Variations

Cutting with the critical angle in mind helps cutters understand where and when they have to stop, or where they have to cut to have the best results. The light must be reflected on the inside facets of the pavilion, bounce around a little, and then come back towards the crown/table.

For example, a spinel will typically be cut with a deeper pavilion than a diamond. Quartz, beryl, zircon and topaz are other stones that you often find with a deep belly. Otherwise, they will be windowed or dark. Moissanite can be cut shallowly enough without getting a window. Its critical angle is low, but that doesn’t mean it is the best angle to cut it at!

Dependent on the Jewelry Design

Sometimes, the cut has to fit the jewelry setting, so the cutter must respect the dimensions asked, no matter the type of stone. That can sometimes result in an asymmetrical or subpar cut. If the space in the setting is too cramped or the prongs are too short, the lapidary artist may have no choice but to cut a shallow stone to fit inside. Commercial quality jewelry will often have shallow stones set in order to save on production costs. In these cases, the results are obvious to the trained eye – windows, windows everywhere!

Repair Work

An example of cutting for repair work might involve a ring or other piece of jewelry that loses or breaks its stone and a replacement is needed. Most of the time, commercial quality jewelry will be set with commercial quality gems. This means that the original gemstone may not have had the best cut. So, when a replacement is needed, the lapidary artist doesn’t have a lot of legroom. They cut miracles when they can, otherwise, they cut the gem to fit.

Optical Phenomenon and Color

Sometimes, the color in a gemstone will not be evenly distributed. When faced with color zones, a cutter has to make some choices. The placement of the facets will ultimately impact the color and therefore, the value of the gem. This dilemma often happens with sapphires, citrines, amethyst and tourmaline, among others. The same thing will happen with optical phenomena, such as pleochroism, or gems with asterism and cat’s-eye. The cutter must be very careful with the direction of the cutting, the angle with the best color, and/or the angle at which the inclusions must be in order to have the best cat’s-eye possible after the stone is cut.

In-Depth Knowledge

It’s important to understand why the depths of a gem can be so different from one another in order better evaluate the gemstone. Knowledge is power in the jewelry business. After all, customers don’t simply want jewelry. They want a story with bits of information and trivia sprinkled in with well-placed wisdom. Gemstones offer these multi-faceted stories.

All images are courtesy of the author unless otherwise indicated. ◊

The post Cutting It Close and Critical appeared first on Incolor Magazine.