International Gem Society

Dedicated to bringing quality information and educational services to everyone interested in gemstones.

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HOW GEMS ARE IDENTIFIED
by Don Clark CSM

... People frequently ask me to identify their gems. Often they think that I can do this by simply looking at them. I can once in a while, but that is a rarity.
... In most cases assigning the correct name to a gem is a matter of detective work, finding clues and eliminating possibilities. The clues are physical and optical properties of the gem. Each time I measure or observe one of these properties, the number of possible gems I could be looking at gets smaller. I keep gathering more information until I have a set of properties that can only belong to one gemstone.
... For example, let’s say some one asks me to identify a red stone. (The question is probably phrased, “Is this a ruby?”) Now, I should know a ruby when I see one, right? Well, sometimes I can be pretty sure if a gem is a ruby or not just by a quick observation. However, I can’t tell if it is natural or synthetic without a more detailed observation. Even if I am “pretty sure” the gem is a ruby, I would be reluctant to say so.
... I know that there are hundreds of minerals that have been cut as gemstones, most of which can be red. Sometimes that is their primary color, sometimes it is a rarity, but color alone tells me nothing. If the gem is transparent that cuts the list in half, still not much help.
... To identify this red stone I am going to need something more useful than color and transparency. The most helpful information I can have are the properties known as refractive index and specific gravity. If I know one of these, the list of gems that could have that property is immediately reduced to a dozen or two. If I know both of these the list may well be under ten possible gems.
... From here the tests I perform, the next set of properties to identify, will depend on what possibilities still exist. Some information will be much more useful than other, some no good at all, depending on the circumstances. The choices I have include spectroscopic analysis, determining double refraction, optic sign, pleochroism and reaction to UV.

... Such is the science of gemology. By taking enough measurements I can start with a list of hundreds of possible minerals and systematically eliminate possibilities down to one. Or so I hope! :-)
... There is a point where gemology becomes an art, where the final determination is made by human observation, (combined with knowledge and experience,) rather than measurements taken with precision instruments.
... This is particularly true when it comes to separating natural from synthetic gems. A synthetic ruby will have the identical set of measurable physical and optical properties it’s natural counterpart does. The separation is made by observation of inclusions with a microscope. In some cases this is simple and straight forward, but at other times it requires judgment based on experience. Microscopic details are subtle!

... If you are a novice gemologist, I hope you have learned two things from this. First, what the basic procedures are to identify gems. Second and most importantly, that a little information can be a dangerous thing.
... While learning gemology is a worthwhile endeavor, you shouldn’t make an expensive decision based on limited knowledge. Also, you should be cautious who you trust to identify your gems.
... Most jewelers have limited experience in colored stones. If they have a Graduate Gemologist degree, that means they are well trained in methodology and the use of instruments. However, their training only covers the 100 or so gems that are most likely to show up in jewelry. While they may be able to identify the more common gems, they occasionally come across minerals that are outside the range of their experience and their reference materials.
... If you would like to learn more about gemology, you can contact your local college or university. Some of them have courses available. The Gemological Institute of America has an excellent correspondence course. A word of caution though, this is both expensive and difficult. It is not something to be taken lightly.
... If your interest is more casual, or your time too restricted, then I suggest you become a member of the International Gem Society. Here information is presented in common language, inexpensively and there is no pressure to perform.

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