Telling apart different gemstones is often a challenge for people new to the collection and study of gemstones. After all, there’s a whole field of study dedicated to doing just that! Fortunately, if you’re up to the challenge you only need to know a few things to tell apart stones, even when they bear similar coloration like alexandrite and amethyst.
So, let’s expand your gemmy horizons and discus alexandrite versus amethyst, how to tell them apart, and then we’ll cover some common questions about both!
An In-Depth Look at Alexandrite
Alexandrite is a specific form of the mineral chrysoberyl. As one of the three main forms, it’s also the rarest. Most chrysoberyl is a yellow-green in color, very similar to peridot while cymophane is a bright yellow stone which often displays the cat’s eye effect (chatoyancy.)
Color-Changing Phenomena in Alexandrite
Alexandrite, on the other hand, is known primarily as a reddish-purple, blue-purple, or purple stone. It houses a bit of a secret, however, since the gemstone changes color depending on the lighting in which you’re looking at it. The exact color of the stone varies quite a bit, but in general the value of natural alexandrite is based on the normal four C’s (color, clarity, carat weight, and cut) with the addition of the color change. The more dramatic the change, the more expensive the stone.
Why is Alexandrite So Valuable?
Alexandrite is well-suited for jewelry. At a hardness of 8.5 on the Moh’s scale, the stone is even harder than beryl-type gemstones like emerald and morganite. This makes it well-suited for use in jewelry that may come into contact with things on a regular basis, such as rings and bracelets.
True gem-grade alexandrite is found in only a few places across the world, with the highest quality material generally being considered that from the Urals in Russia. The Russian material rarely makes it to the market these days, however, and you’re far more likely to see material from Brazil or Tanzania.
It’s among the most expensive gemstones, despite technically being a “semiprecious” stone. It’s important to remember that “precious” simply refers to the classic gemstones (diamond, ruby, emerald, sapphire) rather than the actual value of the stone.
Alexandrite is a fast favorite for many. You’ll hear various descriptions of the color changing traits of the stone, often things like “emerald by day, amethyst by night” due to the effect of lighting on the stone’s dominant hue. In theory, a true green to red transition would be the most valuable stone but these are insanely rare, even taking into consideration of the rarity of this beautiful, color-shifting mineral in the first place.
The color change is due to chromium being included in the crystalline lattice of the mineral, replacing aluminum. It’s distinct from pleochroism, which relies on the angle of light entering the stone to change its color. Instead, the chromium adds a green color to the stone but certain forms of light make it less apparent so that the stone instead shows its purple or red coloration outside of full spectrum daylight.
How To Tell if Alexandrite Is Real
In examining the authenticity of alexandrite gemstones, one must consider various indicators to determine if the stone is genuine. To identify real alexandrite, a gemologist or jeweler typically assesses these specific characteristics:
- Color change – Real alexandrite looks green in daylight but red under lamps
- Few flaws – Real alexandrite has very few blemishes or inclusions
- Where it’s from – Natural alexandrite mainly comes from Russia, Sri Lanka, Brazil
- Hardness – Real alexandrite is very hard and resists scratching
- Additional Tests – Experts use tests like spectroscopy to check the stone’s makeup
Firstly, the color-changing property is a crucial aspect of genuine alexandrite; it exhibits a distinct transformation between green in daylight and red under incandescent light.
Additionally, the gem’s clarity is carefully inspected, as real alexandrite should have minimal inclusions or blemishes.
Another crucial factor in determining authenticity is the stone’s origin, with natural alexandrite primarily originating from mines in Russia, Sri Lanka, and Brazil.
The stone’s hardness is also assessed on the Mohs scale, indicating whether it can resist scratching.
Lastly, expert gemologists may employ advanced testing techniques such as spectroscopy and thermal conductivity measurements to confirm the stone’s composition. By examining these various aspects, one can effectively discern if an alexandrite gemstone is genuine or not.
Exploring the Properties of Amethyst
Origins and Abundance of Amethyst
Amethyst is the purple form of quartz. Quartz is among the most common minerals on the planet, but the various forms are certainly pleasing to the eye. A few hundred years ago amethyst was considered one of the precious stones, with a value comparable to ruby and sapphire. European amethyst primarily came from the Urals, which is still considered to be the location of some of the best amethyst in the world.
Quartz, and thus amethyst, is a very simple mineral. It’s comprised of silica, which itself only contains silicon and oxygen. It forms many of the favorite stones for rockhounds, from citrine and amethyst to other, much more complex mixtures such as agates and jaspers. Amethyst is generally macro-crystalline, appearing as clusters, points, and hollow nodules.
The coloration of amethyst comes from iron trapped in the crystal lattice of the stone. Citrine and prasiolite bear roughly the same impurities. Citrine is formed at a higher temperature than amethyst, while prasiolite comes in between in a very narrow band of temperatures. In fact, most of the citrine sold on the market as both gemstones and mineral samples was pulled from the Earth as amethyst and heat treated at a later date.
The Color and Hardness of Amethyst
Amethyst has a hardness of 7 and is known to be a bit fracture prone compared to similar gemstones. Ask a stone setter about how nerve-wracking it can be to close the prongs on one of these stones if you want more detail in that regard.
Amethyst fell out of it’s classic designation as a precious gemstone due to the discovery of large deposits in the Americas. It’s found in dozens of locations across the USA, but the majority of material is mined in Brazil.
There, amethyst is found in large basalt formations. Most of the samples you’ll see are mined from there, the distinctive grey of the basalt from the region is a dead giveaway in most cases. It’s not uncommon to see geodes large enough to fit a grown adult in museums these days, and virtually all of these larger formations come from that region.
While this has cheapened samples and low-to-mid grade amethyst quite a bit, higher grade amethyst is still hard to find and can be rather expensive. It’s not going to compare to the “classic” gemstones, and it’s certainly orders of magnitude cheaper than alexandrite, but a few carats of Siberian amethyst with a deep purple and red undertones won’t come cheap either.
Related: Dig Your Own Amethyst Crystals: The Diamond Willow Mine
Comparing Alexandrite and Amethyst: Similarities
These stones, on occasion, bear similar coloration. This certainly isn’t true in all cases, but there are certainly times where an alexandrite seen in the correct lighting will resemble an amethyst strongly. That said, alexandrite more often bears blue undertones than the red which typifies the best amethyst.
Both are also commonly used in jewelry from rings to necklaces.
Amethyst is pleochroic, meaing the color can change depending on the angle of the light entering the stone, but this quality is only seen in minor ways. Still, both can have changing colors, although alexandrite is much more dramatic in this regard.
Differences Between Alexandrite and Amethyst
Physical and Social Differences
When it comes to anything other than incredibly superficial qualities like coloration, these stones couldn’t be more different. Their differences are vast, from basic physical properties (alexandrite has a much higher specific gravity and is quite a bit harder, for instance) down to their social qualities.
Alexandrite is generally considered a very high-end stone, enough that it’s commercially viable for both synthetic and simulant material to be commonplace. On the other hand, amethyst is almost never sold in a synthetic form due to the high availability of the stone in many places across the planet.
Size and Rarity
Even their size in nature is quite different. While amethyst crystals can be found weighing kilograms, and are often cut into enormous gemstones, alexandrite occurs only in small amounts. The largest cut alexandrite, for instance, is a bit shy of 70 carats. Impressively large, but nothing compared to some of the cut amethyst available which can weigh in excess of 200 carats or more.
Alexandrite vs Amethyst FAQ
Q: Is there synthetic alexandrite?
A: Synthetic alexandrite is common. If the price you’re seeing for a given gemstone seems reasonable, and you’re not the type of person who owns a super-yacht, then you’re looking at a synthetic or simulant stone. The synthetic variety is chemically identical to “real” alexandrite, but is usually made with the Czochralski method. This method generally leaves the stone with high clarity, although others are flux-grown and may show inclusions similar to natural forms of the mineral.
Q: Is there fake alexandrite?
A: Simulants differ from synthetics, in that they mimic the look of the natural mineral without having the same chemical structure. Simulant alexandrite can be found made from color-changing glass or vanadium-laced corundum. Both can be determined with a hardness test, and the corundum variety will never display the green tones found in most true alexandrite.
Q: What about fake amethyst?
A: While it’s certainly possible to synthesize amethyst, as well as most quartz varieties, it’s rarely done with the intention to pass it off as other material. Amethyst is plentiful enough, even in the higher grades, that it’s just not going to be a big money maker. On the other hand, heat-treated amethyst is often passed off as citrine. This is a common enough practice that anyone buying faceted citrine would do well to just assume it’s heat-treated amethyst. The practice is so common that it doesn’t require disclosure in most cases.
Q: How much is alexandrite worth?
A: Gem-grade, natural alexandrite will generally run from $8,000 to $15,000 per carat. The price increases steeply after this, and by the time you hit 2 carats or more you’ll most likely be looking at a six-figure stone. Synthetic material often runs from $50-$500 per carat depending on the quality of the synthesis and it’s coloration.
Q: How much is amethyst worth?
A: In a cut form, amethyst has a huge range of pricing. It can run from pennies per carat to $120. The price of Siberian amethyst, which has become a catch-all for deeply saturated purple material, can run a bit higher and will increase steeply after the first few carats if there’s a lack of color zoning in the final gemstone.
Q: What determines the price of an alexandrite?
A: The biggest factor, apart from the normal qualities, is the coloration of the stone. Natural alexandrite often bears yellowish or brownish tinges to the blue-green and red-purple coloration at the opposite ends of the spectrum. Higher color saturation with a less muddy hue will naturally command higher prices.
Q: Is alexandrite suitable for everyday wear?
A: Absolutely. For the most part, alexandrite is hard enough you’re unlikely to encounter anything that will scratch it in day-to-day life. The only minerals which are harder are corundum (ie: rubies and sapphires) and diamonds. Just try not to scrape it with one of those and it won’t scratch, and the stone is rather durable although not impervious to chipping or shattering.
Q: Is amethyst suitable for everyday wear?
A: To some degree. It’s fine in pendants and earrings, but the hardness of amethyst is only a 7.0 on the Moh’s scale. It should be worn with care as well, since it’s rather fracture prone compared to many gemstones. As long as you’re not digging in sand or bashing it against stones and metal it will generally be fine but it’s rather easy to damage compared to the classic gemstone families like beryl and corundum.
