Chrysoberyl Group
Alexandrite
Alexandrite performs a genuine and dramatic color-change trick — green to bluish-green in daylight, shifting to red or purplish-red under warm incandescent light — caused by a real, unusual absorption spectrum rather than any illusion, first documented in the Ural Mountains of Russia in the 1830s and named after the future Tsar Alexander II.
The geology — what Alexandrite actually is
- Mineral class
- Oxide (chrysoberyl group)
- Chemical formula
- BeAl2O4, with trace chromium
- Crystal system
- Orthorhombic
- Mohs hardness
- 8.5
What causes the color: Trace chromium substituting for aluminum creates an absorption spectrum with two nearly equal transmission windows, one in the green and one in the red — daylight (rich in blue-green wavelengths) shows the stone as green, while warmer incandescent light (rich in red wavelengths) shifts the balance toward red, a genuine, physically documented optical phenomenon rather than a trick of perception.
How it forms: Forms in rare geological settings where beryllium-rich fluids interact with chromium-bearing rock, typically in mica schist near contact zones — a genuinely uncommon combination of elements that don't usually occur together, which is exactly why fine alexandrite is so rare.
- Ural Mountains, Russia (the original 1830s discovery locality, now largely depleted)
- Brazil
- Sri Lanka
- India (Andhra Pradesh)
Treatments & imitations: Natural, untreated alexandrite is highly valued and relatively rare; a substantial share of 'alexandrite' on the market is actually lab-grown or is color-change synthetic corundum or spinel doped to mimic the effect, which should always be disclosed as synthetic rather than natural.
Real vs. fake: Genuine natural alexandrite shows its color shift alongside pleochroism (different colors from different viewing angles even under one light source) and Mohs 8.5 hardness; synthetic color-change corundum or spinel imitations often show a more abrupt, less nuanced color shift and different inclusion patterns under magnification.
Most of what is sold under this name was grown in a lab
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- Lab-grown alexandrite, disclosed as synthetic
This page says outright that most available jewellery uses laboratory material, and that it must be disclosed as synthetic. Bought knowingly, it is chemically the same chrysoberyl at Mohs 8.5; bought unknowingly, it is a misrepresentation.
- Paired daylight and incandescent lamps
The colour shift only exists as a comparison between two named light sources, so judging any stone of this species needs both. The page notes the shift is a permanent physical property rather than something that wears off.
The tradition — how people use Alexandrite
Historical use: Alexandrite's 1830s Russian discovery and naming after the future Tsar Alexander II is well documented, and its red-and-green color shift took on particular significance in Imperial Russia since those colors matched the military colors of the Russian Imperial Guard.
Metaphysical tradition: Modern crystal-healing tradition frames alexandrite as a stone of transformation and balance, an interpretation drawn directly and specifically from its genuine, scientifically documented color-changing property.
How to use it: Faceted for fine jewelry given its exceptional hardness and rarity; because natural fine-quality material is genuinely scarce and expensive, most alexandrite jewelry available today uses lab-grown material, which should be clearly labeled as such.
Cleansing & care: At Mohs 8.5, alexandrite is very durable and suitable for daily wear; clean with mild soap and water, and note that its color shift is a permanent physical property, not something that fades or requires special maintenance.
Frequently asked questions
Is alexandrite's color change a real physical property?
Yes, genuinely — it comes from a documented, unusual absorption spectrum caused by trace chromium, giving the stone two nearly equal transmission windows (green and red) that shift in visual dominance depending on the light source's color temperature. It's real optics, not an illusion or a trick of perception.
Related crystals
Cat's Eye Chrysoberyl
Chrysoberyl Group
Cat's eye chrysoberyl is, gemologically speaking, the original and definitive 'cat's eye' stone — when jewelers refer to a chatoyant gem simply as 'cat's eye' without naming the mineral, this is historically the material meant, and every other chatoyant stone (tiger's eye, cat's eye quartz) must be specifically qualified by name to avoid that assumed default.
Spinel
Oxides
Spinel carries one of gemology's most fascinating cases of mistaken identity: for centuries, red spinel was sold and worn as ruby, and several of history's most famous 'rubies' — including the Black Prince's Ruby in the British Imperial State Crown and the Timur Ruby — have since been identified as spinel instead.
Emerald
Beryl Group
Emerald shares its exact base mineral, beryl, with aquamarine and morganite, but it's dramatically rarer than either, and the reason comes down to a genuine geological coincidence: beryllium (needed for any beryl) typically occurs in silica-rich granite, while chromium and vanadium (needed for emerald's green) typically occur in silica-poor mafic rock — two chemistries that almost never form in the same place, which is why fine emerald is so much scarcer than blue aquamarine despite being the same underlying mineral.
Sources and factual basis for the geology above: see our methodology.