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What is Tanzanite Pleochroism?

by Steve Moriarty April 02, 2018

Are you a little more scienticially minded? Well we have received a few questions about Pleochroism with the topic of Tanzanite. First of all let's talk about what Pleochroism actually is and how it affects Tanzanite.


Pleochroism is the ability to show different colors in different directions of the crystal. Tanzanite is a rare crystal in that it is a trichroic gemstone. This is because Tanzanite shows blue in one direction, purple in another direction and finally yellow in the last direction. This makes it a very colorful gemstone and why you see so many different colors of Tanzanite.


When we get the rough Tanzanite from the mines, we normally heat the gemstone. Why do we heat Tanzanite? We want to change it from a trichroic gemstone to a dichroic gemstone. Basically we want to get rid of the yellow color from the gemstone. In the rough, the gemstone looks more red-brown in color and then after it's heated it goes to a blue-purple color.


It really depends on when you see it. When you travel to a jewelry store, you see it in it's dichroic form. With us, we really see it in it's Trichroic form, because we see the stone before it's heated.


Hi. I'm Steve Moriarty from You can shop us
online for fine tanzanite or in Crown Point, Indiana at our store,
Moriarty's Gem Art.

One of the questions I get from those that are a little more scientifically
minded, or you may have heard discussions of pleochroism and tanzanite.
Pleochroism is tanzanite's ability to show different colors in different
directions of the crystal. Tanzanite is unusual in that it is a trichroic
gem, and it shows blue in one direction, purple in another, and yellow in
another direction.

Now, from the rough crystal we generally heat the material, and our purpose
of heating is to change it from trichroic to dichroic. We're getting rid of
the yellow color, and it's going from what looks kind of brownish red in
the rough crystal and it goes to the blue purple, because we've removed the
yellow color from it.

I once had a discussion with Gordon Liddicoat, who wrote the handbook on
gemstone identification, as to whether the book was right in saying that
tanzanite is trichroic. You know, by the time you or a jeweler sees the
stone, it's been heated and there is no longer any yellow color in it, so
in my opinion it is now a dichroic stone. I don't know the true answer to
that. I would be interested if any of you have any input on "Is tanzanite
in the cut form dichroic or trichroic?"

Well, that's my explanation of pleochroism. So, shop us online at or in Crown Point, Indiana at Moriarty's Gem
Art. Thank you.

Steve Moriarty
Steve Moriarty

Steve Moriarty has been in the jewelry industry for over 30 years. Steve is not only a jeweler, but a gem cutter and designer. He has traveled the world in search of gemstone rough and has owned a retail jewelry store for 20 years located in Crown Point, Indiana.

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