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How to Identify a Natural Alexandrite

Justin Zaroovabeli
March 25, 2024

Are you trying to figure out how to recognize a natural alexandrite? Focus on the gem’s signature color transition and distinctive inclusions. This guide will walk you through these indicators, and the physical tests used to authenticate a real alexandrite. Plus, we’ll touch on when it might be time to consult an expert, giving you confidence in your gem’s authenticity without overwhelming you with details upfront.

Decoding the Alexandrite Effect

GIA stones in both green and red hues
Image Credit: GIA

The unique and inherent characteristic of the mineral chrysoberyl variety, alexandrite, is its association with the color-change phenomenon. This dramatic shift from bluish green in daylight to a purplish red under incandescent light is what truly sets alexandrite apart.

Alexandrites that display a robust color change with vibrant color saturation, especially in the blue green spectrum, are the most sought-after.

Daylight vs. Artificial Light

Alexandrite displays different hues under varying lighting conditions. For instance, under incandescent lighting, such as that from a lamp or candle flame, it exhibits a brownish or purplish red color. More intriguing is the fact that ultraviolet light, including both long and shortwave, can reveal fluorescence or phosphorescence in natural alexandrite, serving as additional identification markers. Under fluorescent light, the color change can be even more pronounced, adding to the gemstone’s allure.

The Color Change Phenomenon

The term ‘alexandrite effect’ is used to describe the remarkable shift in color from bluish green in daylight to purplish red under incandescent light. Synthetic alexandrites often display less pronounced color changes than their natural counterparts due to the challenge of duplicating the natural geological conditions in a laboratory setting.

Unveiling Inclusions: Nature's Fingerprint

green natural alexandrite

The unique natural fingerprint of inclusions in natural alexandrite helps differentiate it from lab-created alexandrites and other synthetics. These inclusions can include:

  • fluorite
  • apatite
  • mica platelets
  • rutile
  • multi-phase inclusions
  • negative crystals
  • liquid inclusions
  • fingerprint inclusions

It’s also interesting to note that synthetic alexandrites, a type of synthetic corundum, and synthetic spinel may contain distinctive gas bubbles and curved striations, which are absent in natural stones.

Visible Inclusions Under Magnification

The visible inclusions under magnification are key to identifying natural alexandrite. Natural alexandrite inclusions do not show curved growth lines, which are typical of synthetic counterparts. Jewelers utilize specialized equipment to uncover these inclusions and confirm if an alexandrite is natural.

By using microscopes to closely study the inclusions within alexandrite, gemologists can distinguish between natural and synthetic gems.

Types of Inclusions Unique to Natural Stones

Geologically formed natural alexandrite contains distinct inclusions that signify its natural origin. However, synthetic imposters such as flux grown synthetic alexandrite can have inclusions that mimic those of natural stones. This similarity in inclusions often necessitates professional gemological analysis to accurately identify natural alexandrite.

Measuring Physical Properties: More Than Just Size

round natural alexandrites in both hues

Real alexandrite, characterized by a refractive index between 1.746 and 1.755, can be authenticated based on this specific physical property. Additionally, natural alexandrite is known to be doubly refractive, unlike some synthetic versions which may not exhibit this characteristic.

Refractive Index Test

Gemologists use a refractometer as a vital tool to measure alexandrite’s refractive index, a key characteristic for its identification. The property of birefringence, a characteristic of doubly refractive gems like natural alexandrite, can be measured using a refractometer, aiding in distinguishing natural stones from synthetic counterparts.

Specific Gravity and Hardness

Specific gravity, a useful metric in gem identification, is the weight of a gemstone relative to that of an equal volume of pure water at 4°C. To ascertain a gemstone’s specific gravity, the stone is weighed in air and then in water, with the specific gravity determined by dividing the weight in air by the loss of weight in water according to Archimedes’ principle.

Accurate specific gravity testing requires the gemstone to be devoid of surface substances and the water used to be distilled, deionized, and free of surface tension.

Rarity and Origin: The Geological Heritage

oval shaped purple natural alexandrite

Alexandrite was first discovered in emerald mines near the Tokovaya River in the Ural Mountains in 1834. This discovery held significant symbolism as the gem’s color transformation from green to red mirrored the national military colors of Imperial Russia. After the Russian sources were exhausted, significant new deposits were found in Brazil in 1987.

Following the find in Brazil, additional sources were uncovered in Sri Lanka and East Africa, expanding its availability beyond the original Russian locality.

Traceability and Provenance

The historical significance and the pronounced color change of the original Russian alexandrites are pivotal factors that assist in tracing and determining the provenance of these gemstones.

A gemological certificate serves as a crucial document to confirm the natural origin of an alexandrite and verify whether it has undergone any treatments, thereby ensuring its authenticity and underlying value.

The Rarity Factor

Even the lower quality stones of natural alexandrite gemstones, rarer than diamonds, are deemed scarce and costly. The value of a natural alexandrite is greatly influenced by the extent of its color change; stones exhibiting a full green to purple-red shift are considered exceptionally rare and valuable.

Fine-quality natural alexandrite is considered practically unaffordable by the general public, underscoring its rarity and the high demand for such gemstones, especially in alexandrite jewelry.

Consulting the Experts: Seeking Professional Verification

a pair of pear shaped natural alexandrites

Verification of a natural alexandrite’s authenticity necessitates engagement with a professional gemologist, owing to their expertise. Professional gemologists utilize specialized equipment and advanced techniques that are not typically available to most consumers, ensuring a more thorough and accurate assessment.

Importance of Certification and Lab Reports

To ensure the authenticity of an alexandrite gemstone, it is essential to obtain a lab report from a recognized gemological institute. A GIA Colored Stone Identification & Origin Report for alexandrite includes assessments of:

  • Weight
  • Measurements
  • Shape
  • Cutting style
  • Color
  • Detectable treatments
  • Opinion on geographic origin

The Role of Specialized Equipment

To identify natural alexandrite gems, expert gemologists employ specialized equipment like gemological microscopes and spectroscopy devices. Using magnification equipment, experts analyze the type and presence of inclusions, which are key in distinguishing natural alexandrite from synthetic ones.

The Impact of Cut and Carat: Assessing Gem Quality

blue green oval alexandrite

A well-cut alexandrite displays the most potent color change through the crown, achieved by the gem cutter orienting the rough stone to highlight both colors when viewed from the front. Because of the complexity of maximizing the color change, high-quality alexandrites with good cuts are rare and thus command premium prices.

The Cut's Influence on Color Shift

Maximizing the visibility and intensity of the color change effect in an alexandrite is highly dependent on its cut. To optimally showcase the alexandrite’s color change, the stone should be cut in such a way that:

  • The strongest color change is visible face-up from different angles
  • The stone is not too deep or shallow, as this can affect the color change
  • The facets are well-proportioned and symmetrical

By considering these factors, you can ensure that the color change in your alexandrite is maximized and truly stunning.

Significance of Carat Weight

Due to their scarcity, larger alexandrites are inherently more valuable than smaller ones, with the gem’s price significantly influenced by its carat weight. High-quality alexandrites exceeding one carat can command prices upward of $15,000 per carat, with those in the 2.00 to 5.00-carat range being priced over $25,000 per carat.


In conclusion, identifying a natural alexandrite gemstone involves a comprehensive understanding of its unique color change phenomenon, careful examination of its inclusions, accurate measurement of its physical properties, and an appreciation of its rarity and geological heritage. It also necessitates professional verification to ensure its authenticity. The allure of alexandrite lies not only in its captivating color change but also in its rarity and the mystery surrounding its origins.

Frequently Asked Questions

How can I tell if my alexandrite stone is real?

To determine if your alexandrite stone is real, there are several methods you can employ. One way is to examine its color change phenomenon, which is a hallmark of genuine alexandrite. Place the stone under different lighting conditions, such as daylight and incandescent light, and observe if it exhibits a noticeable shift in color. Additionally, you can conduct a visual inspection for any natural inclusions or imperfections, as real alexandrite often contains these characteristics. Furthermore, obtaining a reputable certification from a gemological laboratory, such as GIA or AGL, can provide assurance of the stone's authenticity. Finally, consulting with a qualified gemologist or jeweler can offer valuable insights and expertise in verifying the genuineness of your alexandrite stone.

How rare is natural alexandrite?

Natural alexandrite is exceptionally rare, making it one of the most coveted and valuable gemstones in the world. Its rarity is attributed to several factors, including its limited geographical occurrence and the specific geological conditions required for its formation. Additionally, the unique phenomenon of color change exhibited by alexandrite further enhances its scarcity and desirability. As a result, natural alexandrite commands high prices in the gemstone market and is highly sought after by collectors and enthusiasts alike.

What is the color change phenomenon in alexandrite?

The color change phenomenon in alexandrite, often referred to as the "alexandrite effect," is a captivating optical phenomenon observed in this rare gemstone. Under different lighting conditions, alexandrite displays a remarkable shift in color, typically from greenish-blue in daylight or fluorescent light to purplish-red in incandescent light. This mesmerizing transformation is caused by the presence of trace elements, particularly chromium, within the crystal structure of the alexandrite. These elements interact with light in a unique way, resulting in the absorption and reflection of specific wavelengths, thus creating the distinct color change effect. 

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