A multi-colored andradite, or possibly a demantoid?
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  A multi-colored andradite, or possibly a demantoid?

by Guy Borenstein, FGA
September 20, 2012

A demantoid is a very rare and precious variety of the andradite garnet series. Its name, which is derived from Dutch, means "diamond-like," and it refers to the exceptional quality of this gem and its unique brilliance and fire.

The demantoid colors typically range from Yellow-Green (10) to Green (14). Therefore, it considered as "the king of the green garnets."

Recently, we had the opportunity to test the color of a unique multi-colored andradite garnet gem, offered for sale by Allen Brown from All That Glitters (http://www.atggems.com). The 2.71-ct. emerald-cut gem displays attractive color zoning with green and yellow colored stripes. Since "regular" demantoid gems are known to be scarce, you may probably guess how rare this piece is.

The gem was sent to the GIA lab for identification, prior to our analysis and received an interesting result. The GIA certificate stated that this is an andradite garnet, without noting the demantoid variety name. Further explanation given by the GIA lab director, revealed the reason. The GIA cannot identify it as a demantoid because demantoid gems are supposed to be green, and green only!

We took several images of the multi-colored gem and analyzed each of its color areas separately to get the three components and their ratio within the gem. After deconstructing the color, we used GemeGrade, a grading feature of our GemePrice™ pricing system, to compare each of the retrieved colors with its andradite variety definition.

The color analysis results showed three color components. The largest colored area (33.44%) was identified by the system as medium very slight grayish Yellow Green (10-6-3). The smaller areas were identified as very dark slight brownish Yellow (8-8-2, 30.31%) and light strong strongly yellowish Green (11-3-5, 25.94%).

Comparing the components using GemeGrade proves that the green area indeed corresponds with the demantoid definition. However, the yellow area was found to correspond with the general andradite garnet (without the specific variety name). The smallest area, made of strongly yellowish Green color, was closer to the demantoid definition, but the green shade was not sufficiently dominant.

The GemeGrade results offer us a reasonable explanation why the GIA lab could not define it as a demantoid. Although the major color component, the medium very slight grayish Yellow Green, corresponds with the demantoid colors, its portion within the gem is small - less than half of the gem area.

According to our analysis, "multi-colored andradite" is a better-suited name for this remarkable and rare gem.