Russian alexandrite displaying green to red colour change.
Alexandrite is a very rare stone that is known for its spectacular colour changing properties; under daylight conditions the stone appears green, while under incandescent light it appears a purplish-red hue. The first major alexandrite deposits were found in 1830 in Russia’s Ural mountains. Alexandrite caught the country’s attention because its red and green colours mirrored the national military colours of imperial Russia. The gem was named after the young Alexander II (1818–1881), the heir to the throne.
Most prized are those alexandrite birthstones that show a vivid green to bluish green in daylight or fluorescent light, and an intense red to purplish red in incandescent light. The spectacular Ural Mountain deposits were eventually mined out, and now most alexandrite comes from Brazil, Sri Lanka and East Africa. The newer deposits contain some fine-quality stones, but many display less-precise colour change and muddier hues than the 19th century Russian alexandrites. Because of its scarcity, especially in larger sizes, fine-quality alexandrite is one of the more expensive coloured gems.
The largest faceted alexandrite is 65.7 carats and was mined in Sri Lanka, and it resides at the Smithsonian Institution.
SOURCES:
“June Birthstones.” GIA, www.gia.edu/birthstones/june-birthstones#birthstone_3.