Identifying genuine natural alexandrite requires a combination of visual assessment, scientific measurement, and professional expertise. The alexandrite market has long been plagued by misrepresentation, with synthetic corundum, synthetic spinel, and lab-created alexandrite all being sold, sometimes knowingly and sometimes unknowingly, as natural alexandrite. Having worked exclusively with natural alexandrite since 2006, and having examined thousands of stones over nearly two decades, we want to share the knowledge that separates informed buyers from vulnerable ones.
The most reliable method of identification is always professional gemological testing with a GIA report. However, understanding the visual and physical characteristics that distinguish natural alexandrite from its imitators can help you make better decisions before reaching that stage.
Natural alexandrite is identified by three things working together: a true colour change — bluish-green in daylight to reddish purple under candlelight in a dark room — an independent laboratory certificate confirming natural origin, and a seller willing to document both. Synthetics and colour-change look-alikes imitate the effect but not the chemistry; a GIA report settles the question. If any one of the three is missing, treat the stone as unverified.
True natural alexandrite changes colour: bluish-green in daylight, reddish purple under candlelight in a dark room. The change is distinct, not a faint shift.
A certificate from an independent gemological laboratory (GIA) is the only reliable proof of natural origin — ask for it before any purchase.
Most "colour-change" stones sold online are synthetic alexandrite or colour-change sapphire and spinel; a laboratory report tells them apart.
Rarity sets the price: a large stone at a small price is a warning, not a bargain.
Buy from a seller who names the stone's origin, provides certification, and puts return terms in writing.
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Watch this natural alexandrite shift from green to purple as the lighting changes:
Visual Assessment: What to Look For
Size and clarity together are your first clue. Natural alexandrite is GIA Type II, meaning inclusions are expected. A large (over one carat), eye-clean alexandrite with vivid color change should immediately prompt scrutiny. Such stones are not impossible in nature, but they are extraordinarily rare and extraordinarily expensive. If the price does not match that rarity, the stone is almost certainly not what it claims to be.
Examine the color change character. Natural alexandrite typically shifts between bluish-green or teal and reddish purple or violet-purple. The transition is real and visible but tends to be nuanced rather than stark. Synthetic alexandrite, particularly Czochralski-grown material, often displays a more dramatic shift to intense, almost neon colors. Synthetic corundum sold as alexandrite typically shifts between blue-gray and pinkish-purple, colors that are distinctly different from genuine alexandrite’s range.
Lighting conditions matter for assessment as well. To properly evaluate an alexandrite’s color change, you need to view it under the right conditions: candlelight in a dark room for the purple, and natural daylight for the cool color. Under mixed lighting or standard bright household bulbs, even a genuine alexandrite with strong color change may appear muted or grayish, which can be misleading. If the light source is too bright, some green will almost always remain visible regardless of the bulb type.
Under magnification (10x or higher), look for the types of inclusions present. Natural alexandrite may contain needle-like rutile inclusions, fingerprint patterns from healed fractures, mineral crystals such as mica and apatite, and stepped or angular growth zoning. Synthetic stones may show curved growth lines, gas bubbles, or flux remnants, none of which occur in nature.
Physical Properties for Identification
Natural alexandrite has a refractive index between 1.746 and 1.755 and is doubly refractive (birefringent). This can be measured with a refractometer, a standard tool in any gemological laboratory. Synthetic corundum sold as alexandrite simulant has a refractive index of 1.762 to 1.770, measurably higher. Synthetic spinel simulant is singly refractive with an index of approximately 1.73. These differences are subtle but definitive when measured with proper equipment.
Specific gravity is another distinguishing property. Natural alexandrite’s specific gravity ranges from 3.70 to 3.78. Corundum sits at 3.99 to 4.00, a significant difference detectable by hydrostatic weighing. These measurements are straightforward for any equipped gemologist but impossible for a consumer without specialized tools.
When Professional Testing Is Essential
While visual and physical assessments can raise or lower suspicion, they cannot provide certainty. Flux-grown synthetic alexandrite can be particularly deceptive because it may contain inclusions that mimic natural features and has identical refractive index and specific gravity. Only advanced spectroscopic analysis, such as the testing performed by GIA, can definitively separate flux-grown synthetics from natural stones.
Our firm recommendation: for any alexandrite purchase over $500, insist on a GIA Colored Stone Identification and Origin Report. The cost of the report is negligible compared to the risk of paying natural alexandrite prices for a synthetic or simulant stone. At The Alexandrite, every piece ships with GIA certification included at no additional cost, because we believe this is an ethical necessity, not a premium service.
Frequently Asked Questions
Can I identify real alexandrite at home?
You can look for clues: whether the stone has visible inclusions, whether the color change is nuanced rather than extremely vivid, and whether the price is consistent with natural alexandrite’s rarity. View the stone by candlelight in a dark room for the best color change assessment. However, definitive identification requires professional gemological testing.
What is alexandrite’s refractive index?
Natural alexandrite has a refractive index between 1.746 and 1.755 and is doubly refractive. This distinguishes it from synthetic corundum (1.762–1.770) and synthetic spinel (approximately 1.73), both commonly used as alexandrite simulants.
Leon Boucheron
Gemologist
With over 21 years specializing in rare colored gemstones, Leon Boucheron has authenticated alexandrite specimens for collectors worldwide. Every piece at TheAlexandrite.com is personally verified for natural origin and quality.
