Alexandrite was first discovered in Russia in the early 1800's. It was named in honor of Alexandar Nicholavich, who was later to become the Russian Czar Alexander II. Legend has it that the gemstone was discovered on the future Czar's birthday and named in his honor, though the factual nature of this is disputed. The unique color change habit of Alexandrite is caused by slight impurities of the element chromium. The most desirable colors of Alexandrite are those that show a clearly visible pure hue color change, such as a pure green/blue in daylight to a pure red in incandescent light. In addition to its color-changing habit, Alexandrite is a pleochroic gem, showing different color intensity when viewed at different angles. This factor must be taken into account when cutting Alexandrite gemstones. Alexandrite exhibiting chatoyancy does exist but is very rare, thus Alexandrite Cat's eye is rarely available.