Cat’s eye diaspore, also known as diasporite, also empholite, kayserite, or tanatarite, is an aluminium oxide hydroxide mineral, α-AlO(OH), crystallizing in the orthorhombic system. And isomorphous with goethite.
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It occurs sometimes as flattened crystals. But usually as lamellar or scaly masses, the flattened surface being a direction of perfect cleavage. The lustre is markedly pearly in character. Diaspore is colorless or elso greyish-white, also yellowish, sometimes violet in color. And it varies from translucent to transparent. It may be visibly different from other colorless transparent minerals. With a perfect cleavage and pearly luster like mica, talc, brucite, and gypsum by its greater hardness of 6.5 – 7. The specific gravity is 3.4. When heated before the blowpipe it decrepitates violently, breaking up into white pearly scales.
The mineral occurs as an alteration product of corundum or emery. And it is found in granular limestone and other crystalline rocks. Well-developed crystals are found in the emery deposits of the Urals. And at Chester, Massachusetts. Also in kaolin at Schemnitz in Hungary. If obtainable in large quantity, it would be of economic importance as a source of aluminium.
Diaspore, along with gibbsite and boehmite, is a major component of the aluminium ore bauxite.
Csarite, ottomanite, and zultanite are trade names for gem-quality diaspore, also known as Turkish diaspore, from the İlbir Mountains of southwest Turkey.
Cat’s eye effect
In gemology, chatoyancy, chatoyance or cat’s eye effect, is an optical reflectance effect seen in certain gemstones. Coined from the French “oeil de chat”, meaning “cat’s eye”, chatoyancy arises either from the fibrous structure of a material, as in cat’s eye tourmaline, or from fibrous inclusions or cavities within the stone, as in cat’s eye chrysoberyl. The precipitates that cause chatoyance are the needles. Examined samples have yielded no evidence of tubes or fibers.The needles precipitates all align perpendicularly with respect to cat’s eye effect. The lattice parameter of the needles matches only one of the three orthorhombic crystal axes of the chrysoberyl, as a result of an alignment along that direction.
The phenomenon resembles the brilliance of a silk spool. The luminous streak of reflected light is always perpendicular to the direction of the fibres. For a gemstone to show this effect better, the shape must be a cabochon. Round with a flat base, rather than faceted, with the fibers or fibrous structures parallel to the base of the finished gem. The best finished specimens show a single sharply. A band of light that moves across the stone when it turns. Chatoyant stones of lesser quality display a banded effect as is typical with cat’s-eye varieties of quartz. Faceted stones do not show the effect well.
Cat’s eye diaspore from Turkey. Video