Thursday, December 25, 2008
 Translucent yellowish chatoyant chrysoberyl is called cymophane or cat's eye. Cymophane has its derivation also from the Greek words meaning 'wave' and 'appearance', in reference to the chatoyancy sometimes exhibited. In this variety, microscopic tubelike cavities or needlelike inclusions of rutile occur in an orientation parallel to the c-axis producing a chatoyant effect visible as a single ray of light passing across the crystal. This effect is best seen in gemstones cut in cabochon form perpendicular to the c-axis. The color in yellow chrysoberyl is due to Fe3+ impurities.
Although other minerals such as tourmaline, scapolite, corundum, spinel and quartz can form "cat's eye" stones similar in appearance to cymophane, the jewelry industry designates these stones as "quartz cat's eyes", or "ruby cat's eyes" and only chrysoberyl can be referred to as "cat's eye" with no other designation.
Gems lacking the silky inclusions required to produce the cat's eye effect are usually faceted. An alexandrite cat's eye is a chrysoberyl cat's eye that changes color. "Milk and honey" is a term commonly used to describe the color of the best cat's eyes. The effect refers to the sharp milky ray of white light normally crossing the cabochon as a center line along its length and overlying the honey colored background. The honey color is considered to be top-grade by many gemologists but the lemon yellow colors are also popular and attractive. Cat's eye material is found as a small percentage of the overall chrysoberyl production wherever chrysoberyl is found.
Cat's eye really became popular by the end of the 19th century when the Duke of Connaught gave a ring with a cat's eye as an engagement token, this was sufficient to make the stone more popular and increase its value greatly. Until that time, cat's eye had predominantly been present in gem and mineral collections. The increased demand in turn created an intensified search for it in Ceylon. Early 20th century prices could go up as high as $8000 for a cut stone
Monday, December 15, 2008
Some gemstones are manufactured to imitate other gemstones. For example, cubic zirconia is a synthetic diamond simulant composed of zirconium oxide. Moissanite is another example. The imitations copy the look and color of the real stone but possess neither their chemical nor physical characteristics.
However, lab created gemstones are not imitations. For example, diamonds, ruby, sapphires and emeralds have been manufactured in labs to possess identical chemical and physical characteristics to the naturally occurring variety. Synthetic (lab created) corundums, including ruby and sapphire, are very common and they cost only a fraction of the natural stones. Smaller synthetic diamonds have been manufactured in large quantities as industrial abrasives. Larger synthetic diamonds of gemstone quality, especially of the colored variety, are also manufactured.
Whether a gemstone is a natural stone or a lab-created (synthetic) stone, the characteristics of each are the same. Lab-created stones tend to have a more vivid color to them, as impurities are not present in a lab, so therefore do not affect the clarity or color of the stone. However, natural gemstones are still considered more valuable on average due to their relative scarcity.
The origin of the gemstone also does not affect its categorization as precious or semi-precious. Rubies, sapphires and emeralds are always precious stones, while other gems are considered semi-precious.
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