Alexandrite

Alexandrite is a rare variety of the mineral chrysoberyl that exhibits a remarkable color change. Under daylight or fluorescent light, it typically appears emerald green or teal, while under incandescent light (like candlelight or tungsten bulbs), it shifts to a raspberry red or purplish-red. This phenomenon is known as the 'Alexandrite Effect' and is caused by the complex way the stone absorbs light due to trace amounts of chromium.

Formation & Geology

Alexandrite forms in a very specific geological environment where beryllium and chromium meet. This is rare because these two elements are usually found in different types of rocks. It typically occurs in pegmatites and mica schists. The most famous historic deposits were in Russia's Ural Mountains, but today it is also mined in Brazil, Sri Lanka, and East Africa.

Physical Characteristics

With a Mohs hardness of 8.5, alexandrite is extremely durable—second only to sapphire and diamond among popular gemstones. It has good toughness and no distinct cleavage, making it an excellent choice for everyday jewelry. The quality of the color change (how distinct the shift is) is the primary factor in determining its value.

Historical Significance

Named after Tsar Alexander II of Russia, alexandrite was discovered in the Ural Mountains in the 1830s. Because its colors (red and green) matched the military colors of Imperial Russia, it became the national stone of the Tsarist Empire. It is one of the birthstones for June, often shared with pearl and moonstone.

Natural vs. Synthetic Alexandrite

Because natural alexandrite is so rare and expensive, many stones sold as "alexandrite" in tourist jewelry shops are actually synthetic color-change corundum (sapphire) or synthetic spinel. These simulants usually change from purple to blue, rather than the distinct green-to-red of natural alexandrite. Lab-grown alexandrite (chrysoberyl) also exists and is chemically identical to the natural stone but much more affordable.