The natural art of ametrine
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FIGURE 1: The polished ametrine with an unusual stepped zoning structure (left), compared to a more typical specimen of ametrine (right).


FIGURE 2: A rare 'trapiche'-like pattern in a rough ametrine crytsal.

  The natural art of ametrine

by Guy Borenstein, FGA
May 6, 2012


We recently received for analysis several images of some remarkable ametrine. They came courtesy of L. Allen Brown, the owner of All That Glitters from Methuen, MA (www.atggems.com).

Ametrine is a bi-colored variety of quartz, composed of amethyst, with purple hues, and citrine, with yellow to orange hues. Almost all polished ametrine gems are fashioned in an emerald-cut style to emphasize the color border. The gemstones commonly are purple at the bottom of the crystal and orange at the top. Natural ametrine comes exclusively from the Anahi Mine in Bolivia, which is supposed to be the only mine producing Ametrine. The mine also produces amethyst and citrine.

The images that were received by the Gemewizard® Color Report were of polished ametrine and rough crystal specimens. They displayed unusual color distribution, for while the colors were typical for ametrine, the border between the colors was atypical. We thus decided to inspect the color arrangement within each gem.

At first, we took the polished ametrine (emerald cut, 18.39 X 12.41 X 7.61 mm, 13.91cts) and compared it with an ametrine that displays regular color distribution (emerald cut, 17.49 X 12.97 X 11.40mm, 20.27cts). As seen in Figure 1, we noted that although the color distribution in the unique ametrine displayed a stepped zoning structure, the colors remain approximately the same as in the regular ametrine. What we had was a rare collector's piece, because the stone clearly displays a distinct step-like border, without harming the vivid saturation of each separate color.

Next, we took one of the amazing rough ametrine crystals (3.5 inches in height and a weight of approximately 834 carats, and we checked its color distribution. Inspecting the specimen from the top and from side-view, we discovered (as seen in Figure 2) a rare "trapiche"-like pattern of citrine orange stripes with the amethyst purple color between them. These beautiful stripes cross the crystal perpendicular to the c-axis in three directions, according to the crystal structure. This pattern is rare and the stone could be considered as a museum piece.

By analyzing the color of the orange stripes, we found reddish tint, hinting that, during the analysis, the color might be merged with a purple background (because of the view angle). Based on the orientation of the stripes, the only view angle that could produce clear orange stripes will be from the top (parallel to the c-axis), but in this case it was not applicable.

We suspect that by slicing this collector piece we could reveal a perfect six-ray 'trapiche' pattern of color distribution (as illustrated in Figure 2). However, we totally agree with Mr. Brown that this is a natural work of art, which should be preserved and not manhandled in any way.

If you have a magnificent gemstone or colored diamond and would like Gemewizard® to analyze it in one of its next Gem Color Reports, please contact us at info@gemewizard.com.