GIA: "NATURAL-COLOR FANCY WHITE AND FANCY BLACK DIAMONDS".

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Date of Publishing: 2023.
No. of Pages: 18.

Natural Fancy white and Fancy black diamonds are not routinely submitted to GIA for grading (fewer than 2,000 since 2008). These fancy-color diamonds are distinctive since the causes of color generally are not atomic-scale defects, but nanometer- to micrometer-sized inclusions that reduce the diamond’s transparency by scattering or absorbing light (some exceptions exist among Fancy black diamonds). To clarify, Fancy white diamonds are those rare stones colored by inclusions that give a “whitish” appearance, and are distinct from “colorless” diamonds on the D-to-Z scale. These two colors, often thought of as opposites in the color world, are grouped here as outliers within the colored diamond world. Both can be colored by inclusions so numerous the stone would fall below the I3 grade on the clarity scale, demonstrating that inclusions, often perceived as a negative quality factor, can create a distinctive appearance. Among the Fancy white diamonds examined for this study, the vast majority (82%) were type IaB, making them a rare subset of a rare diamond type. Based on prior geological research, these are surmised to be mostly sublithospheric in origin (i.e., forming more than 250 km below the earth’s surface). The Fancy white diamonds generally have a different chemistry from D-to-Z type IaB diamonds, with greater quantities of several hydrogen- and nickel-related defects. Among Fancy black diamonds, the major causes of color are either micrometer-sized dark crystal inclusions, nanometer-sized inclusions clustered into clouds, or a combination of the two. For these two colors of diamond, we summarize their gemological properties along with the absorption and luminescence spectra of a representative subset of diamonds from each color, examining how they deviate from the standard grading methodology. Because of their rarity, there has been very little systematic study of either of these color categories, and never a sample set of this quantity, which includes data for ~500 Fancy white and ~1,200 Fancy black diamonds.

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Contents:

1. Causes of Color.

2. Spectroscopy.

3. Gemological Observations.

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