Alexandrite

The Gemstone That Changes With the Light

One Crystal. Two Colours. A Masterpiece of Optical Physics.

Few gemstones demonstrate the relationship between light and matter as dramatically as alexandrite.

Under daylight or cool white illumination, alexandrite may appear green, blue-green or teal.

Under warm incandescent illumination, the same crystal may appear red, purple-red or raspberry.

The gemstone has not physically changed.

Its crystal structure remains the same.

What changes is the spectrum of the light entering it—and therefore the wavelengths returned to your eyes.

This remarkable phenomenon is known as:

The Alexandrite Effect

Alexandrite does not simply possess a colour.

It interacts with its environment to reveal more than one.

The Mineral Behind the Transformation

Alexandrite is the colour-change variety of the mineral chrysoberyl.

Its chemical formula is:

Beryllium Aluminium Oxide

BeAl₂O₄

Pure chrysoberyl is generally colourless to pale yellow or greenish.

Alexandrite forms when small amounts of chromium enter the chrysoberyl crystal lattice, replacing some of the aluminium ions within its structure.

This apparently minor chemical substitution fundamentally changes the way the crystal absorbs visible light.

The result is one of the most extraordinary optical effects in gemology.

The Chromium Connection

Alexandrite and ruby are both coloured principally by chromium.

Yet they do not look the same.

Ruby is chromium-bearing corundum.

Alexandrite is chromium-bearing chrysoberyl.

The chromium ions occupy different structural environments in the two minerals. Because the surrounding atoms and bond geometries are different, chromium interacts with light differently in each crystal lattice.

In ruby, chromium strongly favours the transmission and emission of red light.

In alexandrite, chromium creates strong absorption through the yellow-green region while leaving two important transmission regions:

• one in the blue-green region;

• and another in the red region.

The apparent colour depends on which part of the incoming light spectrum is strongest.

The same colouring ion can therefore produce two dramatically different gemstones because it is held within two different crystal structures.

Chemistry provides the ingredient.

Crystallography determines the result.

Why Alexandrite Changes Colour

Daylight contains a relatively broad distribution of visible wavelengths, including substantial blue and green light.

Under daylight or daylight-equivalent illumination, alexandrite commonly appears:

• Green

• Blue-green

• Teal

• Greenish blue

• Yellowish green

Traditional incandescent light contains proportionally more red and orange wavelengths and less blue light.

Under warm incandescent illumination, alexandrite may appear:

• Red

• Purplish red

• Raspberry

• Reddish purple

• Pinkish red

This colour change is not a pigment switching on and off.

It is the combined result of:

• chromium-related selective absorption;

• the spectral composition of the light source;

• the orientation of the crystal;

• the path length travelled by light through the stone;

• the strength of the colour-producing absorption;

• and the response of human colour vision.

The finest alexandrite appears distinctly green under cool light and distinctly red under warm light.

Other stones may display more subtle transitions, such as teal to purple, greenish grey to raspberry or yellow-green to reddish violet.

Each crystal presents its own interpretation of the alexandrite effect.

More Than a Simple Colour Change

Alexandrite possesses two related but distinct optical properties:

Colour Change

Colour change occurs when the same gemstone is viewed under light sources with different spectral compositions.

For example:

Daylight → Green or teal

Incandescent light → Red or purple-red

Pleochroism

Pleochroism occurs when an anisotropic crystal displays different colours when viewed along different crystallographic directions.

Alexandrite is strongly pleochroic and may show different combinations of:

• Green

• Yellow-orange

• Red

• Purple-red

These effects are related, but they are not the same.

Colour change depends principally on the illumination.

Pleochroism depends principally on crystal orientation.

In a faceted alexandrite, both phenomena interact. The apparent face-up colour is influenced by the orientation selected by the cutter and by how light travels through the finished gemstone.

A Crystal With Three Optical Directions

Chrysoberyl belongs to the orthorhombic crystal system.

It is optically biaxial and possesses three principal refractive indices.

This means that light behaves differently along three mutually perpendicular optical directions within the crystal.

Unlike cubic zirconia, which is ideally isotropic, alexandrite has direction-dependent optical properties.

This anisotropy contributes to:

• strong pleochroism;

• directional colour differences;

• measurable birefringence;

• and the importance of cutting orientation.

A cutter cannot consider shape and weight alone.

The crystal must be oriented carefully to balance colour change, brightness, pleochroism and finished yield.

The wrong orientation may weaken the apparent colour change or produce an excessively dark stone.

The right orientation can reveal the crystal at its most dramatic.

The Importance of Light

Alexandrite should never be judged under a single light source.

Its appearance may differ substantially under:

• Natural daylight

• Cool white LED light

• Warm white LED light

• Fluorescent light

• Incandescent light

• Candlelight

• Mixed indoor illumination

Modern LEDs also vary widely in their spectral output. Two lamps with a similar stated colour temperature may not produce exactly the same visual response.

For this reason, an alexandrite may look different in a jewellery shop, beside a window, beneath household lighting or outdoors.

This is not inconsistency.

It is the defining character of the gemstone.

Alexandrite makes the spectrum of its environment visible.

Natural Alexandrite: A Geological Improbability

Natural alexandrite is exceptionally rare because its formation requires an unusual combination of geological conditions.

The host environment must provide the elements needed to form chrysoberyl:

• Beryllium

• Aluminium

• Oxygen

It must also introduce sufficient chromium to create the colour-change effect.

Beryllium-rich geological systems and chromium-rich rocks are not commonly associated with one another. Their intersection requires an unusual geological setting.

This helps explain why fine natural alexandrite is one of the rarest coloured gemstones.

The most celebrated historical material came from Russia's Ural Mountains, although important deposits have also been found in Brazil, Sri Lanka, East Africa and other regions.

Large, transparent natural crystals displaying a strong green-to-red change are exceptionally uncommon.

Lab-Grown Alexandrite: Real Alexandrite

At Gemdrop®, we offer genuine laboratory-grown alexandrite.

Lab-grown alexandrite is not merely a purple colour-change stone.

It is not glass.

It is not cubic zirconia.

It is not colour-change sapphire.

True lab-grown alexandrite is chromium-bearing chrysoberyl with the alexandrite colour-change effect.

It possesses essentially the same:

✓ Chemical composition

✓ Chrysoberyl crystal structure

✓ Chromium colouring mechanism

✓ Orthorhombic symmetry

✓ Refractive-index range

✓ Birefringence

✓ Pleochroism

✓ Hardness

✓ Colour-change physics

The primary difference is origin.

Natural alexandrite crystallised through geological processes within the Earth.

Lab-grown alexandrite crystallised under carefully controlled technological conditions.

The mineral physics remains the same.

Not Every “Alexandrite” Is Alexandrite

The name alexandrite has historically been applied loosely within the jewellery market. Some stones sold as “synthetic alexandrite” are actually colour-change synthetic sapphire [corundum-alexandrite].

Colour-change sapphire can be attractive, but it belongs to the corundum family and has a different:

• Chemical composition

• Crystal structure

• Refractive index

• Specific gravity

• Optical character

• Absorption spectrum

True alexandrite is chrysoberyl:

BeAl₂O₄

Colour-change sapphire is corundum:

Al₂O₃

A visual colour change alone does not establish that a gemstone is alexandrite.

The underlying mineral must be identified.

At Gemdrop®, material identity is treated separately from appearance. A stone is described as alexandrite only when the available evidence supports chromium-bearing colour-change chrysoberyl.

Transparency begins with naming the gemstone correctly.

How Lab-Grown Alexandrite Is Made

Growing alexandrite is technically demanding.

The process must create a high-quality chrysoberyl crystal while introducing chromium at controlled concentrations and maintaining suitable growth conditions.

Several growth technologies have been used to produce synthetic alexandrite.

Czochralski-Grown Alexandrite

The Czochralski process grows a single crystal from a high-temperature melt.

During growth:

• Chrysoberyl-forming components are melted under controlled conditions.

• A precisely oriented seed crystal is brought into contact with the melt.

• The seed is slowly rotated and withdrawn.

• Material crystallises onto the seed.

• A large alexandrite crystal gradually develops.

The chromium concentration, temperature gradient, pulling rate, atmosphere and crystal rotation must all be carefully controlled.

Czochralski growth can produce alexandrite with:

✓ Exceptional transparency

✓ Strong colour change

✓ High optical quality

✓ Excellent colour consistency

✓ Large areas of usable crystal

✓ Outstanding jewellery performance

Under magnification, pulled alexandrite may show curved or undulating growth structures, colour zoning or other features associated with melt growth.

The Science of Crystal Growth

A laboratory-grown gemstone does not emerge instantly from a machine.

It develops through controlled crystallisation.

Atoms and ions must repeatedly reach the growing surface, enter suitable structural positions and become incorporated into an ordered chrysoberyl lattice.

Small differences in:

• Temperature

• Growth rate

• Rotation

• Chemical composition

• Dopant concentration

• Atmospheric conditions

• Thermal gradients

can influence the finished crystal.

These variables may affect:

• Colour

• Colour-change strength

• Zoning

• Transparency

• Internal strain

• Inclusions

• Pleochroism

• Fluorescence

Every lab-grown alexandrite is therefore a product of both mineral chemistry and crystal engineering.

The Strength of the Colour Change

Not all alexandrite displays the same degree of colour change.

A strong colour change requires a careful balance.

If the absorption is too weak, the colours may appear pale or poorly separated.

If the absorption is too strong, the stone may become excessively dark.

The visual result is also affected by the size and cut of the gemstone. A longer path through the crystal increases absorption and may deepen the colour.

This means that a larger alexandrite is not simply a scaled-up version of a smaller one.

The interaction between absorption, path length and facet geometry can alter its entire visual personality.

Colour change may be described by considering:

• the difference between the two apparent hues;

• the proportion of the stone showing the change;

• the strength or completeness of the transition;

• colour saturation;

• brightness;

• and the lighting conditions used.

A dramatic change is not simply “more colour.”

It is a stronger separation between the colours produced under different illumination.

Alexandrite and Fluorescence

Chromium-bearing alexandrite may display red fluorescence under ultraviolet radiation, although its strength varies.

Fluorescence depends on factors including:

• chromium concentration;

• iron content;

• growth chemistry;

• wavelength of ultraviolet excitation;

• and interactions between trace elements.

Iron can suppress chromium fluorescence, so not every alexandrite will respond with the same intensity.

Fluorescence is therefore useful supporting information, but it should not be used alone to identify alexandrite or determine its origin.

No single observation tells the entire story.

Alexandrite Properties

Mineral: Chrysoberyl

Variety: Chromium-bearing colour-change chrysoberyl

Chemical Formula: BeAl₂O₄

Principal Colouring Element: Chromium, predominantly Cr³⁺

Crystal System: Orthorhombic

Optical Character: Biaxial, commonly positive

Mohs Hardness: Approximately 8.5

Refractive Index: Approximately 1.746–1.755

Birefringence: Approximately 0.008–0.010

Specific Gravity: Approximately 3.70–3.75

Pleochroism: Strong; commonly green, orange-yellow and red to purple-red components

Fluorescence: Variable; may display red fluorescence

Cleavage: Distinct to imperfect in certain directions

Durability: Very good

Hard Enough for Jewellery

With a Mohs hardness of approximately 8.5, alexandrite is highly resistant to scratching.

It is harder than emerald, quartz and most other commonly worn coloured gemstones.

It is suitable for:

• Rings

• Earrings

• Pendants

• Bracelets

• Collector Jewellery

• Special-occasion Pieces

• Everyday Jewellery with appropriate care

Hardness, however, is not the same as toughness.

Chrysoberyl can possess cleavage and may still be damaged by a severe impact, particularly near exposed corners, thin girdles or vulnerable facet junctions.

Protective settings are recommended for stones intended for frequent ring wear.

Caring for Alexandrite

Alexandrite can generally be cleaned using:

• Warm water

• Mild soap

• A soft brush

• A clean microfibre cloth

Avoid severe impacts and sudden temperature changes.

Ultrasonic or steam cleaning should be considered only when the gemstone is known to be free from vulnerable inclusions, fractures, coatings or setting-related risks.

When uncertain, gentle hand cleaning is the safest approach.

How Gemdrop® Verifies Alexandrite

Alexandrite identification requires more than observing a colour change.

Each GemDrop® gemstone is assessed using appropriate gemological methods which may include:

• Visual Examination

• Magnification

• Refractive-Index Testing

• Polariscope Analysis

• Pleochroism Assessment

• Daylight and Incandescent-Equivalent Colour Comparison

• Ultraviolet Fluorescence

• Optical Examination

• Specific-Gravity Assessment

• Internal Growth-Feature Analysis

The purpose is to establish the underlying material—not merely to describe its colour.

Where advanced confirmation is required, techniques such as UV-Vis spectroscopy, Raman spectroscopy, FTIR spectroscopy, photoluminescence or compositional analysis may provide further evidence.

Responsible gemstone identification separates:

• what was directly observed;

• what was quantitatively measured;

• what the combined evidence supports;

• and what would require specialist laboratory confirmation.

Every GemDrop® alexandrite receives a unique verification record providing transparent identification and traceability.

Why Choose Lab-Grown Alexandrite?

Lab-grown alexandrite offers:

✓ Genuine chrysoberyl composition

✓ Authentic chromium-based colour change

✓ Strong pleochroism

✓ Excellent hardness

✓ Exceptional optical character

✓ Advanced crystal-growth technology

✓ Greater availability than natural alexandrite

✓ Outstanding value

✓ Transparent laboratory origin

Natural alexandrite is prized partly because geological circumstances made it extraordinarily rare.

Lab-grown alexandrite allows more people to experience the same class of crystal structure and the same extraordinary optical phenomenon.

It transforms rarity into accessibility without removing the science that makes alexandrite remarkable.

The Gemstone of Perspective

Alexandrite carries a lesson unlike that of any other gemstone.

Ruby demonstrates how a trace element can transform a crystal.

Emerald reminds us that complexity and imperfection can create character.

Opal shows how countless microscopic structures can combine to produce extraordinary beauty.

Alexandrite teaches us about perspective.

The crystal does not become something different when the light changes.

It reveals a different part of what was already there.

Under one light, green.

Under another, red.

Neither colour is false.

Neither colour is incomplete.

Both belong to the same stone.

Human beings are often the same.

Different environments reveal different strengths.

A challenge may expose courage.

Responsibility may reveal discipline.

Uncertainty may reveal adaptability.

Kindness may appear when someone else needs it most.

A change in circumstance does not always change who we are.

Sometimes it reveals dimensions that were present all along.

Alexandrite reminds us that identity can be constant while appearance changes, and that understanding something fully may require seeing it under more than one kind of light.

One crystal.

Two colours.

Countless perspectives.

This is alexandrite.

Shop Gemdrop® Lab-Grown Alexandrite

Explore our collection of verified lab-grown alexandrite gemstones in a range of shapes, sizes and colour-change expressions.

Every gemstone includes transparent material identification, disclosed growth information and access to the Gemdrop® Verification Database.