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Bonnot Paris22/9/2026
Alexandrite: The Rare Gemstone That Changes Colour
François Deprez
April 29, 2026
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5 min read
Bonnot Paris · The Precious Stone Journal 2026
Thealexandrite
Green by day, red by night. Why it changes colour, where it comes from, what it really costs—and why we almost never have one in our display cases.
“Emerald by day, ruby by night.” The phrase has been circulating for two centuries, and for once it scarcely exaggerates.
Alexandrite is the only common gemstone whose colour changes distinctly according to the light source: green to bluish green in daylight, red to purple under an incandescent lamp. The phenomenon is so characteristic that it bears its name—we speak of thealexandrite effect for all stones that imitate it.
It is also one of the rarest gems on the market, and one of the most imitated. This article explains what it is, what it is worth, how not to be mistaken—and, in all candour, why you will not find it in our display cases.
01
Identity
One stone, two colours
Alexandrite is neither a sapphire, nor an emerald, nor a garnet. It is a variety of chrysoberyl —a distinct mineral—coloured by chromium, the same element that gives ruby its red and emerald its green.
| Characteristic | Alexandrite | For comparison |
|---|---|---|
| Species | Chrysoberyl | Corundum for sapphire and ruby, beryl for emerald |
| Mohs hardness | 8,5 | 9 for corundum, 7.5 to 8 for emerald |
| Colouring agent | Chromium | The same as in ruby and emerald |
| Everyday wear | Without reservation | Just below corundum, well above emerald |
| Availability | By enquiry | Sapphire is found every day; alexandrite is not |
A point often overlooked: not all alexandrites change colour with the same intensity. The market speaks of a percentage of change — a stone that distinctly shifts from green to red is worth several times more than one that merely turns from green to greenish-brown. This is the primary criterion of value, even before weight.
02
The physics
What produces the effect
The mechanism is elegant, and can be explained in three sentences.
The chromium present in chrysoberyl absorbs light in the yellow part of the spectrum. What remains — green on one side, red on the other — passes through the stone in an almost balanced way. The gem therefore has no intrinsic colour: it reflects the dominant hue of the light source illuminating it.
Under daylight, rich in blue and green, it appears green. Under incandescent light — a candle, a filament bulb — rich in red, it shifts. Modern LED light, depending on its temperature, will produce an intermediate and often disappointing result: this is why an alexandrite should be judged by candlelight as much as by a window.
The same principle elsewhere
Certain purple sapphires display this behaviour: they shift to blue in daylight and purple under a lamp. This phenomenon, sought after by collectors, commands a premium — yet remains infinitely more accessible than in an alexandrite. View purple sapphires →
03
The history
The Urals, and the Tsar
Alexandrite was discovered in the Ural Mountains in Russia, in the 1830s, and named in honour of the future Tsar Alexander II. Coincidence did the rest: green and red were the colours of Imperial Russia, and the stone became a court gem.
These historic Russian deposits are now virtually exhausted. The Ural alexandrites still in circulation are old stones, often removed from period jewellery, and they trade at levels that have little to do with gemmology anymore — one pays as much for provenance as for the stone.
It is a textbook case of what we often repeat: origin influences price, but never on its own. A fine alexandrite from Brazil surpasses an average stone from the Urals, whatever the story accompanying it may say.
04
The deposits
Where are they found?
Current production comes mainly from Brazil, Sri Lanka, Tanzania, Madagascar andIndia. Each origin has its own character — Brazilian stones are renowned for the clarity of their colour change, while those from Sri Lanka are often more generously sized.
In all cases, volumes are incomparable to those of sapphire or emerald. To give a concrete idea: our Beruwala office sees up to three thousand stones per day, of which around ten are selected. A fine-quality alexandrite does not come through every week.
05
Transparency
Why we do not have any
Let us say it plainly, since you will see it anyway as you browse our catalogue: we do not keep a permanent stock of alexandrite. This is not an oversight; it is a decision.
Our method is based on a simple principle: we publish online everything we have, with full characteristics and price. Nearly six hundred stones, from sapphire to tourmaline. A family for which we could offer only one or two gems, renewed according to chance opportunities, does not fit this model — it would create the illusion of a choice that does not exist.
For alexandrite, we therefore work to order. You define the colour, weight, budget and desired intensity of colour change; we consult our purchasing networks and present the stones to you as they arrive, together with their laboratory report. The timeframe is longer than for a sapphire project, and we say so before we begin.
On pricing, a deliberate restraint
We publish price ranges per carat for sapphire and emerald because we have hundreds of stones to assess. We will not publish any for alexandrite : without stock, any range would be copied from elsewhere rather than observed. Ask us for a quote for a specific project; it is more honest.
06
The risk
Synthetics and imitations
This is the real subject of this article, and the reason it is worth reading this far. Alexandrite is one of the most imitated gems on the market, for an obvious reason: rarity creates counterfeiting.
Three situations must be distinguished, and they are not equally serious.
Synthetic alexandrite. Chemically identical, it has long been produced in laboratories. It is not fraud if declared — it is fraud otherwise.
Colour-change synthetic corundum. This is the historic imitation, and by far the most widespread: a laboratory sapphire that shifts from green-blue to violet rather than red. Generations of jewellery have sold it as “alexandrite”. If an inherited antique stone shifts to violet rather than red, the question deserves to be asked.
Natural stones with an alexandrite effect. Some sapphires, garnets or diaspore genuinely change colour. They are real gemstones, entirely legitimate — but they must never be sold under the name alexandrite, which denotes a specific mineral species.
The rule, without exception
For an alexandrite, a report from an independent laboratory is a requirement, not an option — and it must determine whether the stone is natural or synthetic. To the naked eye, the distinction is uncertain even for an experienced professional.
07
The alternatives
Three stones available
If what draws you to alexandrite is a particular colour rather than the phenomenon itself, three families offer it, immediately and with genuine stock available.
If it is green
Emerald
The green of beryl, unmatched in the mineral world. Hardness 7.5 to 8: a protective setting must be considered at the same time as the stone.
5 568 €
If it is red
Ruby
The same chromium as alexandrite, but in a corundum: hardness 9, no cleavage planes, and gemmology’s purest red.
18 528 €
If it is ambiguity
Teal sapphire
Its appearance changes with the lighting: bluer in a display case, greener by a window. A distant cousin of the alexandrite effect, for a fraction of the price.
2 892 €
Loose stones available, prices observed in September 2026.
One emerald engagement ring offers the green of alexandrite in daylight, with a depth that chrysoberyl cannot achieve. A ruby engagement ring offers its evening red, more distinctly—and, incidentally, the same chemical element colours both stones.
As for a teal sapphire engagement ring, it offers what truly appeals to many alexandrite enthusiasts: a colour that refuses to be named, and that is not read in the same way depending on the time of day. This is not a colour change in the gemmological sense— we will never sell it as such —but the effect on the woman who wears it is not so far removed.
08
Frequently asked questions
Alexandrite, your questions
What is alexandrite?
A variety of chrysoberyl coloured by chromium, famous for its colour change: green to bluish-green in daylight, red to purple under incandescent light. Its hardness of 8.5 on the Mohs scale makes it a stone perfectly suited to everyday wear.
Why does it change colour?
Because chromium absorbs light in the yellow part of the spectrum and lets green and red pass through in almost equal measure. The stone then reflects the dominant hue of the light source illuminating it: green under daylight rich in blue, red under warm light.
Where does it come from?
It was discovered in the Ural Mountains, Russia, in the 1830s, and named in honour of the future Tsar Alexander II. The historic Russian deposits are now virtually exhausted: current production comes from Brazil, Sri Lanka, Tanzania, Madagascar and India.
Is it expensive?
Very, particularly above one carat and when the colour change is distinct and complete. We do not keep a permanent stock and therefore do not publish a price range: each alexandrite is the subject of a dedicated search, with a laboratory certificate required.
How can you recognise a genuine alexandrite?
By an independent laboratory report, and by nothing else. The most common imitation is a colour-change synthetic corundum, which shifts from blue-green to violet rather than red. To the naked eye, the distinction is uncertain even for a professional.
Do other stones change colour?
Yes: some sapphires shift from blue to violet, some garnets from green to red, and diaspore from green to pink. These stones are far more accessible, but none should be sold under the name alexandrite — this term refers to a specific mineral species.
Can it be worn every day?
Yes. At 8.5 on the Mohs scale, chrysoberyl sits just below corundum and well above emerald. Clean with lukewarm water and mild soap, and have the setting checked every two years.
The available colours of alexandrite
Emerald · greenRuby · redTeal sapphire · in betweenViolet sapphire · changingTsavorite · vivid green
For a bespoke alexandrite search, everything begins with an appointment. Available stock can be explored from the precious stones.
An alexandrite search?
Tell us the colour, weight and budget: we consult our purchasing networks and present the stones to you as they arrive, with certificate in hand. The timeframe is longer — we tell you so before we begin.
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François Deprez
Founder of Bonnot Paris
