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Z Edit 4 terms found

Z
A grade in GIA’s Color Grading System…. at the end of the “Light Yellow” category. The next color grade for a yellow diamond will put it into the “Fancy (Color) Diamond” category and the price will begin to rise.
Zaire
The former name of the Democratic Republic of the Congo used from 1965 to 1997. Produces a large proportion of the world production of industrial grade diamonds.
Zirconia
Zirconium Oxide, or more accurately Zirconium Dioxide, also called zirconia, when crystallised in cubic system, it is known as Cubic Zirconia. Although this is found in nature, most Cubic Zirconia is made in the lab… hence it is should be more correctly called Synthetic Cubic Zirconia.
Zoning (color zoning)
A term that describes the uneven distribution of color in a gemstone. Zoning is best seen when looking at the stone through the top table facet.