Analyzing tanzanite color using polarizing filters
Home|About Us|Store|Color Report Newsletter|Support|News & Events|Contact|Gemstones Colors

Figure 1: The tanzanite as seen with and without polarizing filter. Courtesy of Advanced Quality ACC (click to enlarge)

Figure 2: The polarized violetish blue color (click to enlarge)

Figure 3: The polarized bluish Green color (click to enlarge)
  Analyzing tanzanite color using polarizing filters

by Guy Borenstein, FGA
February 12, 2012

Tanzanite is a bluish-violet to violetish-blue variety of zoisite. Its color is commonly produced through a heating process, although some unheated blue/violet crystals may be also found. One of the factors for the beautiful blue-violet color is the Pleochroism phenomena of the tanzanite crystal. The crystal structure of tanzanite splits the white light into two or three polarized light rays, each one of them produce a different color. The colors are commonly blue, violet and gray (or brown).

A color that is specific to tanzanite, and one which is desired especially by gem collectors, is a green-violet mixture displayed as an unusual zoning within the crystal. After fashioning and polishing, due to the facets angles, the colors merge and produce a remarkable metallic color.

A 6.31-carat emerald-cut tanzanite, offered by Advanced Quality ACC, was brought to Gemewizard® for color analysis. It exhibited this fascinating phenomenon.

Since its metallic color was clearly visible, we decided to analyze each color component of the gem separately, using a polarizing filter. First, we photographed the gem with the filter, obtaining the first image. Then, we rotated the filter 90 degrees (until it was perpendicularly oriented to the first image) and photographed the second image. The process is depicted in Figure 1.

Each image was analyzed using the Sampler feature of GemePro™. The sampler breaks it down to its color DNA and then produces a Gemewizard® color.

Figures 2 and 3, showing the analysis results of the two polarized images, confirm that the metallic color of this gem is produced by the familiar rich blue-violet tanzanite color, with the addition of a pleasant bluish green. The green color can be eliminated by a heating process, leaving only the violet-blue color within the gem, but then the gem would lose its uniqueness to become a more commonly seen tanzanite.

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