Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia



KORNERUPINE (Kornerupin—Kornerupine—Корнерупин) (Lorenzen, J. 1884), after A.N. Kornerup (1857-1883), Danish geologist.
Silicate – (,Mg,Fe2+)Al4(Mg3Al2)[O4|(OH,F)|Si2O7Si2(Al,B)O10]. Orthorhombic system. Hardness 6.5-7. Density 3.3. Glass luster. Cleavage in one direction. Kornerupine is found in the form of columnar and needle crystals, as well as in columnar, radial-rayed and fibrous aggregates. Color: colorless, white, rose, greenish, yellow, brownish, dark green, olive-green or black.
Deposits. This mineral is typical for metamorphic rocks, rich with Al2O3 and poor with SiO2, and of pegmatites linked with these rocks. In Russia, kornerupine is found on the Kola Penin., at the Makzapakhk deposit of garnet, in the Keivy Range. The first finding of its gem-quality crystals was made in the Aldanskoye deposit of Yakutia in 1998. On alluvial placer, formed at the expense of the erosion of weathering crusts of garnet plagiogneisses, they discovered gravel transparent fragments of crystals of brown-green to dark brown color, up to 1 cm. They display clear pleochroism from brownish-green to brownish-orange and also increased density – 3.37-3.41. The results of researches have shown that Aldan kornerupine was characterized with the high content of iron. Kornerupine, available for faceting, was found in Tadzhikistan, in pegmatites at the Darai-Stazh locality, Pamirs Mts. In the Ukraine, its finding was registered in the Volhynia Region.
First of all, kornerupine was discovered in Greenland, near Fiskenaesset. However, in 1975, only they found gem-quality rough material there. Beside non-transparent bluish-light blue crystals in transformed anortosites they often found dark green crystals up to 25 cm. with transparent segments. In Germany, near Waldheim, Saxony, they discovered a ferrous variety of kornerupine – prismatine, named after the shape of muddy green crystals up to 2 cm. In the south of Madagascar, gem-quality transparent crystals of kornerupine of sea-green color were found for the first time in the Toliara Prov., at the Itrongay deposit. Later, in the region of Betroka, they discovered other deposits with crystals of brownish and green kornerupine, 5x3 cm. in size, from which they made faceted stones up to 21 ct. In 1970s, gem-quality kornerupine was discovered in Tanzania, at the Daluni deposit, in the valley of the Umba River. In Kenya, they found another one large deposit in the Woi Tawet area, near Kwale, with emerald-green crystals up to 10 cm. long, which display the effect of cat’s-eye in cabochons. Color of kornerupine from these deposits depends on the admixtures of vanadium and chromium. Because of strong pleochroism, color of its crystals changes in the day-light from green through light blue to violet one. Besides, findings of kornerupine are known in South Africa, near Port Shepstone, Kvazulu-Natal Prov.; in Namibia, and in Antarctic at the Sell Couw locality. In 1985, in Australia, in the Harts Range, Northern Territories, they discovered a deposit of kornerupine with dark green prismatic crystals up to 20x4 cm. In Myanmar, near Mogok, they extracted brownish-green and green kornerupine in the form of pebbles as an additional material. From it they made faceted stones up to 20 ct. In cabochons they observe sometimes asterism and the effect of cat’s-eye. On Sri Lanka kornerupine from placers in the Weligama, near Matara, was found. It is yellow, green and brown, available for faceting, with strong pleochroism from greenish-yellow to reddish-brown tone. They also found kornerupine cat’s-eye there, which was formed because of inclusions of greenish-black graphite and needles of rutile. In Canada, in the Québec Prov., they discovered the Gatino deposit with large crystals of green to greenish-yellow kornerupine.
Cut Gems. From kornerupine of Sri Lanka they made faceted stones more than 20 ct. in mass. In the Smiths. Inst., Wash., there is a light brown stone from that place in 21.6 ct., a light green one in 15.6 ct. and a brown stone from Madagascar in 10.8 ct. Besides, in these collections there are cabochons of kornerupine cat’s-eye in 11.2 and 9.4 ct. In one of private collections, there is a golden Ceylon kornerupine in 16.5 ct. So, kornerupine, which was supposed to be a rare gemstone earlier, now is known in all the continents.
Similarity. Kornerupine looks like enstatite, epidote and tourmaline.