Alexandrite

Alexandrite is famous for a single, striking optical effect: the same stone reads as green in daylight and red or purplish-red under warm incandescent light. This “alexandrite effect” comes from trace chromium substituting into the crystal structure of chrysoberyl, its parent species, which absorbs light unevenly across the visible spectrum. Daylight is relatively rich in blue-green wavelengths, incandescent light in red-orange, and the stone’s absorption pattern happens to sit right where that shift matters — so it changes color along with the light source rather than simply looking different in different rooms the way any gem does.

Species and variety. Alexandrite is a color-change variety of chrysoberyl (BeAl2O4), the same mineral species behind cat’s-eye chrysoberyl, though the two varieties are prized for different phenomena — chatoyancy in cat’s eye, color change in alexandrite — and a stone rarely shows both strongly.

Discovery and rarity. The stone was first described in the Ural Mountains of Russia in the 1830s and named for the future Tsar Alexander II. Fine natural alexandrite with a strong, clean color change remains genuinely rare and commands prices well above most colored gems of similar size; much of what is sold today as “alexandrite” at accessible prices is lab-created or is a different color-change material (such as color-change garnet or synthetic corundum) marketed loosely under the name, so buyers should ask specifically whether a stone is natural, synthetic, or a chrysoberyl at all.

Hardness and care. At 8.5 on the Mohs scale, alexandrite is highly durable — harder than topaz or quartz, and a practical choice for rings worn daily. Routine cleaning with warm soapy water is safe; ultrasonic cleaners are generally fine for untreated natural stones but worth checking with a jeweler given the material’s cost.

Where it is found. Historic Russian deposits are largely exhausted; modern supply comes primarily from Brazil, with additional material from Sri Lanka, India, Tanzania, and Madagascar. Brazilian alexandrite tends to show a somewhat different, more brownish-green to purplish-red shift than the bluer green of the classic Russian material.

Birthstone role. Alexandrite is a June birthstone only in the US current system (Jewelers of America / AGTA), which added it to accompany the older pearl and moonstone. The historical, US 1912, and UK 2013 lists all give June as pearl and/or moonstone alone — alexandrite is a genuinely 21st-century addition to the June roster, not a revival of older tradition.