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Alexandrite: The Birthstone for June

Rough alexandrite as viewed on incandescent light (left) and on daylight (right)

The month of June is celebrated with three special birthstones alexandrite, moonstone and pearl. As you would guess, alexandrite takes the lead in terms of value, rarity and class; making it our gemstone of focus this month. So, what is it? Why is it so special? Alexandrite is the rare variety of the mineral chrysoberyl (chemical formula BeAl2O4 + Cr) that changes colour in different lighting. In daylight, it’s greenish blue to dark yellow-green, while in incandescent or candlelight, it’s pink to red. This unique mineral was discovered near the Tokovaya River in Russia’s Ural Mountains in the 1830s by mineralogist Nils Gustaf Nordenskiöld who realized the exceptional colour-changing quality.

The stone was named in honour of the then-future Czar of Russia, Alexander II (1818–1881). In addition to its colour-changing habit, alexandrite is a pleochroic gem, showing different colour intensity when viewed at different angles. The colour-changing effect coupled with its beauty, celebrity and rarity have charmed the public imagination about the gemstone, which helped it join the league of birthstones in the 1950s as the modern alternative to pearl and moonstone for June. In some cases, certain types of long, thin inclusions when oriented parallel to each other in alexandrite, creating a phenomenon called chatoyancy or the cat’ s-eye effect. These occurrences are however rare.

Emerald by day, Ruby by Night

Same alexandrite showing drastic colour change in different lighting

Minor impurities of element chromium are responsible for the colour changing the habit of alexandrite. This change is so drastic that the stone is referred to as “emerald by day, ruby by night.” However, alexandrite is very rare and expensive and until recently it was extremely difficult to obtain. New sources discovered since the 1980s in Tanzania, Madagascar, Brazil and India replaced the initials sources of Russia and Sri-lanka, with Brazilian sources being more significant. However, alexandrite remains one of the rarest gemstones. 

Same alexandrite ring and pendant under different lighting

The value of this June birthstone is based on two major factors: First, the closer the colours to pure green (in daylight) and red (in artificial light), the higher the value. Secondly, the more distinct the colours change, the higher the value. Alexandrites can from 100% to just 5% colour change; hence, the most valuable gems would have a 100% colour shift from pure green to pure red. Blue purplish -greens and or brownish reds are less valuable. Clarity is also considered during grading, although most natural alexandrites are not clean. The colour change factor has more effect on value than clarity.

Alexandrite has a hardness of 8.5 on the Mohs scale, with superb toughness and no cleavage (tendency to break when struck). This makes it an excellent jewellery stone for daily wear. If the bride-to-be was born in June, alexandrite would make an exceptional engagement ring. 

Read more interesting articles about minerals and other birthstones on this link: