Jewelry, Gems, & Minerals/Genuine tanzanite


Tanzanite photo
Tanzanite photo  

Tanzanite side photo
Tanzanite side photo  

Is my tanzanite real?

I attached some photos of it to this email.

Thank you.


Hi Kari,

Unfortunately it is always difficult to identify a mineral from pictures. And one of the pictures is very blurry.

Tanzanite is the blue variety of the mineral zoisite, Ca2Al3(SiO4)3(OH), a Calcium Aluminum Silicate Hydroxide. Most tanzanite has a much deeper blue than the color observed in your pictures. However, this may also be the result of bad or indoor lighting or a low calibration CCD of your camera as the picture was taken.

Here is a quick test you may do that may point you in the direction of a true tanzanite. The mineral is highly pleochroic, which means it will act as a natural polarizer of light, thus changing light color depending on viewing angle. As you look at your stone in natural sunlight, rotate it slowly in different directions. Real tanzanite will show three different colors when viewed from different angles, one of these colors will be the blue that made tanzanite famous.

I found this short video on youtube showing the pleochroism in tanzanite.

Natural pleochroism in stones is not that common and restricted to only a few gems, one of those being tanzanite. However, there are other gem minerals that will also show strong pleochroism such as andalusite, iolite, kyanite, kunzite, and titanite, so it is not a 100% determinative test. Yet tanzanite is trichroic, meaning it will show THREE different colors. Other pleochroic gems are only dichroic, exhibiting only two colors.

If your stone exhibits 3 different colors while doing the above test, chances are good that you actually have a real tanzanite.

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Uwe Richard Kackstaetter, Ph.D. (Dr.K)


I can answer questions concerning minerals, mineralogy, gems, metals, and anything that has to do with geology. However, I am NOT a jeweler. Questions about values, settings, gem stone cuts and appraisals are best directed to other experts on this site. I can however aide in the identification of unknown mineral materials. As a public service and part as training for new geoscientists, our university department provides FREE mineral identification for individuals. Please contact me for details or go to for details..


I am a professor of applied geology and mineralogy with many hours of field experience. Furthermore, I enjoy recreational gold prospecting and mineral collecting. As a professor I am engaged in research concerning minerals and their occurrence.

Member of the GPAA (Gold Prospectors Association of America) as well as the Association of Environmental Geochemists. Member of the GSA (Geologic Society of America) Member of the AIPG (American Institute of Professional Geologists)

Here is a small sampling: Mineral-rock handbook: Rapid-easy mineral-rock determination : written for anyone interested in minerals and rocks - Proctor, Peterson, and Kackstaetter;Macmillan Pub. Co. (New York and Toronto and New York) Physical Geology Laboratory e-Manual [CD-ROM], Kackstaetter, Earth Science Education LLC Colorado Front Range Self-guided Geology Field Trips, Kackstaetter,

Ph.D. in Applied Geology and Mineralogy. I am actively teaching courses in mineralogy and a variety of field courses with mineral collecting opportunities. Background in precious metal exploration.

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