Alexandrite, belonging to the gem species chrysoberyl, serves as an alternative birthstone for June. It is a durable and resilient gemstone, with a hardness of 8.5 on the Mohs scale. While chrysoberyl can produce various appealing shades ranging from yellowish-brown to green, it gained significant recognition and popularity for its remarkable cat's-eye phenomenon. This captivating chatoyancy effect is most commonly observed in greenish-yellow cloudy stones, which also exhibit inclusions responsible for the optical effects. This type of chrysoberyl is sometimes referred to as cymophane.
Alexandrite is a rare and sought-after variety of chrysoberyl gemstone with a captivating colour-changing effect. It was first discovered in Russia in the 19th century and is believed to have been named after the Russian Tsar Alexander II. In daylight, Alexandrite gemstones appear blue-green in colour, while in artificial light, they take on a reddish-purple hue.
Rare and highly sought after are good examples of alexandrite gemstones that exhibit a distinct and captivating colour change phenomenon. Different localities showcase subtle variations in this colour change effect. For instance, Brazilian stones often display delightful purplish-red and bluish hues, while Sri Lankan material tends to lean towards an olive colour in the green spectrum. The term "alexandrite effect" is even used to describe the colour change phenomenon observed in other gemstones, highlighting the association of this property with the stone itself.
Alexandrite gemstones with a notable colour change are highly desired and can command high prices, particularly those with larger sizes, excellent clarity, and most importantly, a clear and distinct colour change. Even rarer are alexandrite gems that possess both a colour change effect and an impressive cat's-eye phenomenon. Similar to cymophane, this chatoyancy effect is caused by light being reflected from needle-like inclusions within the gemstone.