What is alexandrite gemstone?
Often referred to as “emerald by day, ruby by night”, alexandrite is a rare gemstone discovered in Russia in 1830*. Alexandrite belongs to the chrysoberyl family of gemstones and is best known for its remarkable colour-changing properties; it appears greenish-blue or green in daylight but changes to a purplish-red or raspberry-red in incandescent light. Whilst generally quite transparent (usually with noticeable inclusions), there is a rare type of more opaque alexandrite which shows chatoyancy or a cat’s eye effect** where a narrow band of light appears to glide across the surface of the stone, resembling the eye of a cat. Alexandrite has a chemical composition of BeAl2O4.
Family: chrysoberyl
Geology: complex, associated with some types of igneous rocks (in form of pegmatites) and some types of metamorphic rock.
Formation: The formation of alexandrite is complex. In simplified terms, a number of certain elements (most noticeably chromium, beryllium and aluminium) must be present during the formation of alexandrite; it is this combination of these elements that creates the unique colour change effect of the stone. To begin with, some chromium must be in the area. Then a mix of liquid and magma begins to form a pegmatite (a type of igneous rock). This now comes into contact with the chromium. As it all cools down a chemical reaction takes place, parts of which involve the chromium ions replacing some of the aluminium ions, and this process forms the alexandrite. To have all these particular elements together in one area and then coming into contact with each other at the same time, is very unusual in nature – which is why alexandrite so so rare.
Colours: various shades of green/ teal (in daylight) to various shades of purplish-red, mauve, and raspberry red, in incandescent light (such as candlelight).
Treatments: usually left untreated
Locations: Alexandrite is rare, but has occasionally been found in small amounts in a few countries around the world, with notable locations including Sri Lanka and Brazil. Historically, Russia produced the best quality alexandrite, and contrary to popular belief there is still Russian alexandrite still being mined, but these are more of a by-product from the mine itself (I believe the mine in question is mainly an emerald and beryllium mine, which also produces many other minerals as a by-product, including some small amounts of alexandrite).
MOHS scale: 8.5
Cool facts and fun: The world of gemstones can be mysterious and murky, and alexandrite is a perfect example of this. Some real controversy exists over the the discovery of this rare gemstone, with sinister goings on over who really discovered and identified it.
Along with this intrigue, some research suggests that during the 1830s powerful Russian figures (who wished to please and integrate themselves politically into the Royal household) pressured a change from alexandrite’s original proposed name ‘”diaphanite” (from a mix of Greek words loosely meaning “two appearances” in reference to its colour change) to “alexandrite” in honour the future Czar Alexander II; they even may have conjured up a tale that alexandrite was “discovered on the heir’s sixteenth birthday”.. even though he only turned sixteen in 1834, four years after alexandrite’s discovery!
Myths and legends aside, in modern times alexandrite is a birthstone for June, and a 55th anniversary celebration stone, and it remains one of the most expensive, rare and desirable gemstones in the world today.
*there is some conflicting information regarding the actual date of alexandrite’s discovery. The Gemological Institute of America writes that it was found in 1830 (GIA sources here, here and here).
**A cat’s eye effect is a visual phenomenon that can occur in certain gemstones, where a narrow band of light appears to glide across the surface of the stone, resembling the eye of a cat. This effect is caused by microscopic needle-like or fibrous inclusions that are present within the crystal structure of the gemstone, and which reflect light in a particular way.
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