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Zircon Cut - a style, based on the brilliant cut, which is designed to improve the brilliance of a zircon. The zircon cut reduces light leakage from the rear of the stone by having an additional eight facets placed between the culet and the main pavilion facets.
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Zirconia - trade name for the man-made diamond simulant cubic zirconium oxide manfactured by Swarovski & Co., of Wattens, Austria. Also the name of a reddish-brown abrasive powder used for polishing gemstones.
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Zoning - straight growth lines of bands with definite angles often seen in crystals.