Kornerupine is a rare gemstone that was first discovered in Greenland in 1887. It was named after the Danish naturalist, artist and explorer Andreas Nikolaus Kornerup (1857-1881). At one time the mineral was also known as prismatine, since the crystals form in long prisms. Kornerupine occurs in a number of colors, including white, pink, yellow, brown, green and blue. Most crystals display a strong pleochroism, usually from yellowish-green to reddish-brown. The emerald green and blue colors are the rarest and most valuable. Some translucent to opaque stones display chatoyancy, the cat’s eye effect. With a hardness rating of 6.5 to 7 on the Mohs scale, kornerupine is hard enough for jewelry. But since kornerupine is so rare, it is mainly a collector’s stone and is not commonly seen in jewelry. Gem-quality specimens are mainly found in small sizes, usually under 2 carats. Clean stones weighing over 5 carats are very rare.