Geographic Origin Determination of Alexandrite

Abstract

GEMS & GEMOLOGY WINTER 2019 A fter the discovery of a gem mineral with unusual color-change behavior in the Russian Ural Mountains during the early 1830s, Swedish mineralogist Nils Adolf Erik Nordenskiöld named this new gem alexandrite in 1834 in honor of the future Czar Alexander II (Kozlov, 2005). This immediately created a royal and romantic aura around this variety of chrysoberyl. The most coveted alexandrites exhibit a lush green to greenish blue color in daylight and a warm, bright red shade in candlelight (Levine, 2008); some fine Brazilian and Indian alexandrite examples are shown in figures 1–3 and 6. This phenomenal color change is caused by the presence of trace Cr3+ substituting for Al3+ in the chrysoberyl crystal structure. Alexandrite is routinely described as “emerald by day, ruby by night.” It is a stone of duality—green or red, cool or warm, day or night (Levine, 2008). Because of its rare and attractive color-change phenomenon, alexandrite has been highly sought after and is one of the most valuable gemstones in the trade. Alexandrite, particularly fine-quality material, is also very scarce; it has generally been a byproduct of mining other major colored stones. Overall production statistics are hard to evaluate. It has been mined in Russia (Kozlov, 2005; Schmetzer, 2010), Tanzania