Guest Author - Susan Dorling

‘Ask Our Gemology Expert’ is a regular feature at the Jewelry Collecting site, kindly provided by our guest contributor, Barbara W. Smigel, PhD., Graduate Gemologist, GIA. As site Editor, my goal is to make the Jewelry Collecting site as comprehensive and interesting as possible for my visitors. Barbara’s expert guidance in this series, and her major contributions to our ‘Everything You Ever Wanted to Know’ series about gemstones, is greatly appreciated and an invaluable learning tool for myself and others who collect gemstones and gemstone jewelry. In fact, the more I learn, the more fascinated I become by gemstones themselves, and their exciting role in jewelry design. Thanks, Barbara!

If you have a question for Barbara, please send an email using our Contact Form with subject line, Ask Our Gemology Expert. And remember, if you would like to learn more about gemology and gemstones check out Barbara's free gemology course, Online Gemology Course. You'll love this fascinating and fun way to learn about gemology.
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This question was sent to Barbara by Terry in Terry, St. Louis, Missouri.

Dear Barbara,

My husband gave me a Tanzanite ring for my 60th birthday. The cut is a marquis. It has a beautiful blue/purple color. However, when I look at the stone from the bottom, it has no color! Is this normal? The ring was purchased from a reputable jewlry store.

Hello Terry,

Yours is a very interesting question. I've thought about it a bit, and can see three possibilities. My usual disclaimer of not being able to make any definitive answer without seeing and testing the gem applies, however.

1) Many stones are colored unevenly (called color zoning). The color we see when we look at a faceted stone from the top may not be its color throughout. The facets cause light to bounce around inside the stone before it exits to your eye and tends to blend the differently colored areas of the stone into a single color. I have seen some pieces of rough that are very light, but when faceted skillfully, because there is a darker area right at the culet (pointed bottom) where most of the reflection occurs, they look much darker as cut stones. It is possible that your stone was highly color zoned and well cut to compensate for it. By turning the stone over you are minimizing reflections and color blending and color zoning would be more visible. I have seen this phenomenon most strongly in amethyst and citrine and also in sunstone and sapphire. I am not familiar with extreme color zoning occurring in Tanzanite, but it is possible.

2) Both Tanzanite and iolite are gems which look different colors from different angles (pleochroic). With Tanzanite the two colors are generally blue and purple. With iolite there are three: a blue-violet color (very similar to Tanzanite color) a grey blue, and a light straw yellow (near colorless). Tanzanite and iolite can sometimes be confused if they are not closely examined. Perhaps the stone is an iolite and when you turn it over and view the bottom you are looking at the near colorless axis.

3) One type of simulated or imitation gemstone is called a doublet. In a doublet the top and bottom of a gem are made of different materials. One of the characteristic features of some doublets is that the top is brightly colored and the bottom is colorless. When these are made to deceive they are generally put in closed settings so the back cannot be observed, but they can be found in prong settings as well.

My suggestion would be to take the ring back to the store where your husband got it and ask to speak to the jeweler or owner (not just a sales clerk). Show him/her the piece and explain your reservations about it -- you might also show them this note. Even if the stone is not what you expected it to be, it might be an honest mistake on their part. The people who supplied them, or those further back in the chain who supplied the supplier, may be at fault. A reputable firm will stand good for their product, no matter who was at fault.

If you end up keeping the ring, let me add that Tanzanite is not a highly durable ring stone. You should reserve the ring for occasional wear as this gem is rather soft and somewhat cleavable. If you want to wear it daily you might consider having the jeweler reset it as a pendant. BTW, I would be very curious to know what you find out from the jeweler.