Cat’s eye kornerupine
Cat’s eye kornerupine, also known as Prismatine, is a rare and beautiful gemstone that captivates gem enthusiasts and collectors alike.
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Cat’s Eye Kornerupine: A Unique and Rare Gemstone
Composition and Crystallization
Cat’s eye kornerupine is a rare boro-silicate mineral, with the chemical formula (Mg,Fe2+)4(Al,Fe3+)6(SiO4,BO4)5(O,OH)2. It crystallizes in the orthorhombic-dipyramidal crystal system, typically forming as brown, green, yellow, or colorless slender prisms reminiscent of tourmaline. The mineral can also be found in massive fibrous formations, adding to its uniqueness.
Physical Properties
This gemstone has a Mohs hardness rating of 7, which makes it suitable for jewelry, while its specific gravity ranges from 3.3 to 3.34. It features indices of refraction as follows: nα = 1.660 – 1.671, nβ = 1.673 – 1.683, and nγ = 1.674 – 1.684. These properties contribute to the gemstone’s impressive optical characteristics and durability.
Formation and Geological Origins
Kornerupine forms in boron-rich volcanic and sedimentary rocks that have undergone high-grade metamorphism. The gemstone can also be found in metamorphosed anorthosite complexes, which add to the complexity and rarity of its geological origins. Cat’s eye kornerupine is commonly found in association with other minerals such as sapphirine, cordierite, spinel, corundum<, tourmaline, grandidierite, dumortierite, kyanite, sillimanite, andalusite, biotite, phlogopite, magnetite, ilmenite, hematite, and rutile.
Valuable and Striking Appearance
Color and Pleochroism
The value of cat’s eye kornerupine lies in its unique appearance and rarity, particularly when it is translucent in green or yellow shades. The emerald-green varieties are especially prized for their vibrant and captivating color. This gemstone also exhibits strong pleochroism, appearing green or reddish-brown when viewed from different angles, adding a fascinating depth to its beauty.
Vitreous Luster and Appeal
Cat’s eye kornerupine is a member of a solid solution series with Prismatine. The gemstone is also known for its vitreous luster, which further enhances its visual appeal when cut and polished. Its strong pleochroic properties and the distinct cat’s eye effect make it one of the most sought-after collector’s gemstones in the world.
History and Discovery
Origins in Greenland
Cat’s eye kornerupine was first described in 1884 after its discovery in Fiskernæs, located in southwest Greenland. It was named in honor of the Danish geologist Andreas Nikolaus Kornerup (1857–1883), who contributed significantly to geological research.
Modern Discoveries
Despite its initial identification in the 19th century, it wasn’t until 1912 that gem-quality material was found. Even today, cat’s eye kornerupine remains a rare find, making it a valuable addition to any gemstone collection.
Cat’s Eye Effect: The Phenomenon of Chatoyancy
Understanding Chatoyancy
In gemology, the term \”chatoyancy\” refers to the optical reflectance effect known as the cat’s eye effect, which is visible in certain gemstones, as in cat’s eye tourmaline or cat’s eye chrysoberyl. Derived from the French term “oeil de chat,” meaning “cat’s eye,” this effect arises due to the fibrous structure of the material or from fibrous inclusions or cavities within the stone. In the case of cat’s eye kornerupine, the chatoyant effect is caused by the alignment of fine, needle-like inclusions within the stone, similar to those found in cat’s eye chrysoberyl.
Mechanism Behind Chatoyancy
The precipitates that cause the chatoyance effect in gemstones are aligned in a direction that is perpendicular to the luminous streak of light visible on the surface. When properly cut into a cabochon—a round shape with a flat base—the gemstone displays a single, sharply defined band of light that moves across the surface as the stone is rotated. The effect resembles the sheen of silk, creating an intriguing play of light that captures the eye.
Quality and Cutting Styles
Higher-quality specimens of cat’s eye kornerupine exhibit a bright, well-defined band, whereas lower-quality specimens may show a more diffuse or banded effect, typical of cat’s-eye quartz varieties. Faceted stones do not usually exhibit the chatoyant effect as prominently as those cut en cabochon, making the cutting style a crucial factor in showcasing the beauty of cat’s eye kornerupine.
Where is Cat’s Eye Kornerupine Found?
Geographical Locations
Cat’s eye kornerupine is typically found in regions rich in boron and metamorphic rock formations. Although it was first discovered in Greenland, deposits have also been located in other parts of the world, including Madagascar, Sri Lanka, Tanzania, and India. Each locality yields stones with unique variations in color, transparency, and chatoyancy, contributing to the gemstone’s charm and desirability among collectors.
Cat’s eye kornerupine from India
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At our gem shop, we offer a wide range of natural gemstones, including the captivating cat’s eye kornerupine. If you’re interested in adding this unique gemstone to your collection, or simply want to learn more about its fascinating properties, feel free to browse our collection.
