Quick answer: Alexandrite is the colour-change variety of the mineral chrysoberyl and the standard against which every other colour-change gem is judged: fine stones are green to bluish green in daylight and red to purplish red under incandescent light — "emerald by day, ruby by night." The change is caused by chromium. Natural fine alexandrite is so scarce it has nearly vanished from the market except as an expensive collector's gem — which is why lab-grown alexandrite, the same mineral with the same colour change, is the realistic way to wear this phenomenon. At Mohs 8.5 it's superbly durable. It's a June birthstone.
What is an alexandrite?
Alexandrite is chrysoberyl — a hard, durable mineral in its own right — with a twist of chemistry: traces of chromium in exactly the right crystal make it transmit two different colour "channels." Which one you see depends on the light feeding it. Discovered in Russia's Ural Mountains in the 1830s and named for the future tsar Alexander II, it became legend fast: a stone wearing imperial Russia's military colours, green and red, in one gem.
How does the colour change work?
Alexandrite's chromium absorbs light in a way that leaves two transmission windows open — one in green, one in red — balanced on a knife's edge. Daylight and fluorescent light are rich in blue-green wavelengths, so the green window wins and the stone looks green to bluish green. Incandescent light and candlelight are rich in red wavelengths, so the red window wins and the same stone turns red to purplish red. The stone never changes; the light does — alexandrite just refuses to compromise between them.
What makes a fine alexandrite?
Three things, in order:
- Strength of the change — the closer to a full green→red flip, the finer. Weak or muddy shifts (khaki→brownish) are the common reality; a clean, dramatic change is the prize. This is the value factor.
- Colour quality — fine stones show green to bluish green in daylight and red to purplish red under incandescent light, at medium to medium-dark tone with moderately strong saturation.
- The usual suspects — clarity, cut and size, amplified by the fact that natural material rarely comes clean and large and strongly changing at once. Russia's historic stones still set the colour standard; fine natural alexandrite today is effectively a collector's market.
How durable is an alexandrite — is it good for an engagement ring?
Superbly. Chrysoberyl rates 8.5 on the Mohs scale — third among classic gem minerals after diamond and corundum — with excellent toughness and no problematic cleavage. An alexandrite handles daily wear as confidently as a sapphire, and its phenomenon makes it arguably the most interactive engagement stone there is: it participates in every candlelit dinner.
Should I buy natural or lab-grown alexandrite?
The honest math: fine natural alexandrite is so scarce that it trades as an expensive collector's gem — when it surfaces at all, strong-change clean stones command prices in ruby territory. Lab-grown alexandrite is real chrysoberyl with real chromium and a real colour change — the same mineral, grown deliberately — at a small fraction of the price. For a stone you intend to wear, lab-grown is the rational modern choice; for a stone you intend to collect, natural with a lab report is the only version that counts. Both deserve to be called alexandrite; neither should be confused with the imitation below.
How can you tell if an alexandrite is real?
First, watch the change itself: test the stone under two lights (daylight or a phone flashlight set cool, then a warm incandescent bulb). Then read the colours.
The classic imitation is colour-change synthetic sapphire — corundum doped with vanadium, sold for a century as "alexandrite" in estate and souvenir jewelry. Its tell is the wrong change: grayish blue to purple-mauve, never the true green-to-red of alexandrite. If grandma's "alexandrite" shifts violet, it's almost certainly this — still a pretty stone, just not the one on the label.
Natural vs. lab-grown alexandrite is subtler: both are chrysoberyl and both change correctly. Natural stones carry natural inclusions (fine silk, fingerprints); some lab methods leave flux veils or curved growth features. That call — and the natural stone's origin — is laboratory work, which is why an important alexandrite should never travel without an independent report. Ours don't.
Why doesn't my alexandrite change colour indoors?
Almost certainly because of your light bulbs. The red side of alexandrite's change needs light rich in red wavelengths — the warm glow of old incandescent bulbs and candles. Modern LED and fluorescent lighting is usually daylight-balanced, so indoors your stone keeps seeing "daylight" and politely stays green. Nothing is wrong with the stone. Want the show? Candlelight, a warm-white (2700K) bulb, or an old-fashioned filament lamp will flip it every time — which is also the correct way to test the change before you buy.
Where does natural alexandrite come from?
Russia's Urals wrote the legend and still define top colour, though the historic mines produce little today. Brazil (a major 1980s discovery briefly revived supply), Sri Lanka and East Africa provide most of what little fine material reaches the market now — scarcity is the through-line of this gem's whole story.
How do I care for an alexandrite?
Like a sapphire: warm, soapy water and a soft brush, with no special sensitivities. At 8.5 hardness with no routine treatments, alexandrite — natural or lab-grown — is one of the most carefree fine gems you can own.
What does an alexandrite mean? (birthstone and symbolism)
Alexandrite is a June birthstone (alongside pearl) and the 55th anniversary stone. Its meaning writes itself: the gem of duality and good omen — logic by daylight, romance by candlelight, in the same stone.
