A variety of Zoisite, tanzanite is the trade name for the transparent blue – violet blue variety. Tanzanite is generally enhanced by heat unless otherwise specified. The unheated crystals can be green, violet, yellowish or, light blue but a brownish root beer color is most common. Heating at 380 degrees C will produce the intense top blue sapphire color. Surprisingly, it is the dark brown crystals that produce the most valuable dark blue stones after heating. The treatment is permanent and accepted in the trade.
Tanzanite is trichroic and exhibits pronounced pleochroism. The colors respective to the three vibrational directions are sapphire-blue, sage green, and purple. Orientation is an important consideration for cutters who need to consider both the yield and the resulting color.
Because of their similarity in color, comparisons between tanzanite and sapphire are inevitable. Fine tanzanites are more affordable and usually better in terms of both color and clarity. However, tanzanites are soft compared to sapphire. Top color sapphires are more rare, much harder, extremely tough and, much more expensive.
Historical tanzanite prices have shown amazing volatility and fluctuations. Wholesale prices for top stones have ranged between $150 to $1000/ct. over the last 20 years. A function of supply and demand, tanzanite prices have always recovered because of their fine color, clarity and affordability.
Grading Tanzanite
We grade and price our tanzanites according to color, size, cut and clarity. Color is the most important factor in determining the value. Most dealers would assess the color component of a stone at between 50 – 70% of its value. In general the best color is bright, rich, and intense. Vivid violetish blue or bluish violet colors are best. Tanzanite can be too dark or too light and the best tones are medium to medium dark. Some dealers describe describe the best colors as AAA.
There is a GIA color guide that rates the colors. This is not a final rule about color grading but it is something the buyer can consider. We color grade our stones according to the closest possible match from the GIA color set.
The guide rates the tanzanite colors as follows on a scale from 1-10: vB 6/5 - 10, bV 6/5 - 8.1, B6/5 - 8.1, vB 5/5 - 6.4, V 6/4, vB 7/5 - 6.4, vB 5/5 6.4 .. and the list goes on but selecting the color you like is more important.
Photographing Tanzanite
Our tanzanites are photographed with cool daylight. We don’t use incandescent lights as they would accentuate the violet components in tanzanite. We do not edit the hue but we may adjust brightness and contrast. Our monitors are set at 50% brightness for working with images. Computer images will show some variation due mostly to monitor settings. For additional clarification, we also verbally approximate tanzanite color. What you see on your screen is probably very close to the actual color but our verbal description may also be useful.
