The name Chrysoberyl comes from the Greek chryso meaning “golden”. During ancient times, Golden Chrysoberyl was considered to be a stand-alone mineral. Green Chrysoberyl, by contrast, was confused with other green gemstones until the advent of modern mineralogy. Chrysoberyls of all colors often show a special affect called chatoyancy, more popularly known as Cat’s Eye. When a stone is cut and polished, a strong, narrow light moves from side to side as the mineral is shifted. This line of light resembles the slit pupil in the eyes of cats, hence the name. The original Cat’s Eye crystal was a form of Chrysoberyl. But today, Cat’s Eyes can also be found in Apatite, Beryl, Moonstone, Opal, and Quartz. When the affect occurs in Ruby and Sapphire it is called a “star” instead.
The most celebrated form of Chrysoberyl is Alexandrite. It was originally found in the Ural Mountains of Russia in the nineteenth century and named in honor of the Russian crown prince, the future Tsar Alexander II (1818-1881). This remarkable stone looks green in daylight but raspberry red under incandescent light. It’s been described as an “emerald by day, ruby by night.” This phenomenon is caused a replacement of aluminum by chromium, which causes light to be absorbed on a narrow range of wavelengths. Because human vision is most sensitive to green light, the gem appears green in the sunshine because we are seeing the full visible light spectrum. But at night, it appears red because incandescent light emits less green light and so our eyes see red instead. Alexandrite does not show this affect under a LED light since it is a full spectrum light source.