Reviewed By Andreas Zabczyk
Kornerupine Rough from Tanzania
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.
By chemical composition, kornerupine is a complex borosilicate that includes magnesium, iron and aluminum. Its crystals form in the orthorhombic system and it has a refractive index of 1.67 to 1.69, similar to that of spodumene. Gem-quality kornerupine is transparent to translucent with a vitreous luster. It is a moderately dense material, with a specific gravity of 3.28 to 3.35, similar to that of tanzanite and diaspore.
Though kornerupine was discovered in Greenland, most of the world's supply has traditionally come from Sri Lanka. The Sri Lankan gems tend to be yellow-green or yellow-brown in color. More recently there have been new discoveries of kornerupine in Tanzania and Madagascar, in rather different colors. The African kornerupine has been found in blue and bluish-green, with a purplish pleochroism. Though the African kornerupine tends to be found in small sizes, the interesting colors have made it more popular for jewelry. Other kornerupine deposits have been found in Australia, Kenya, Burma, Canada and South Africa.
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