• 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.

  • 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.

  • Zoning - straight growth lines of bands with definite angles often seen in crystals.