An Introduction To Gem Identification


Step 1: Introduction to Gemology

Lesson 8

Oval Ruby - gem identification
All rubies are red, (pink is another matter), but not all red gems are rubies. Gem identification involves conducting tests of a gem’s optical and physical properties to narrow a list of possibilities down to one. It also involves observation tempered by knowledge and experience. “Oval Ruby,” 2.16 cts, Sri Lanka. © All That Glitters. Used with permission.

People often ask me about gem identification. More specifically, they ask me to identify their gems. Some think I can do this simply by looking at the gemstones. Sometimes, I can. However, identifying gems is rarely that easy. In most cases, attaching the correct name to a gem requires detective work.

Gem identification involves finding clues and eliminating possibilities. What kind of clues? The optical and physical properties of the gem. Each time I measure or observe one of these properties, the “suspect pool” of possible gems gets smaller. I keep gathering more information until I have a set of properties that can only belong to one gemstone.

Gem Identification 101: The Case Of The Red Stone

Let’s say someone asks me to identify a red stone. (“Is this a ruby?” is the form that question usually takes). Now, I should know a ruby when I see one, right? Well, sometimes I can be pretty sure if it’s a ruby or not just by a quick observation. However, I can’’t tell if it’s natural or synthetic without a more detailed analysis.

Even if I’m “pretty sure” the gem is a ruby, I would still be reluctant to say so after just a quick look. I know there are hundreds of minerals that have been cut as gemstones for jewelry. Most of them can be red. Sometimes that’s their primary color, sometimes it’s a rarity, but color alone tells me nothing. If the gem is transparent, that cuts the list in half. That helps some, but there are still many possibilities.

Red spinel - gem identification
Spinel gemstones come in a wide variety of colors, including red. Historically, some stones classed as rubies were actually spinels. Gemologically, these are now identified as two distinct gem species. At first glance, however, a red spinel can still be confused with a ruby. “Spinel var. red spinel, calcite,” Mogok Valley, Mogok Township, Pyin-Oo-Lwin District, Mandalay Division, Myanmar, by Géry Parent is licensed under CC By-ND 2.0.

To identify this red stone, I’m 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.

Once I’ve narrowed the suspect list down to a dozen or so, the next set of properties I’m likely to identify depends on what possibilities still exist. The choices I have include spectroscopic analysis, double refraction, optic sign, pleochroism, and reaction to ultraviolet light. The information I collect next depends on which properties would best narrow the remaining possibilities. For example, with one red gem, I may choose to learn its optic sign. With another stone, I may opt to determine the gem’s reaction to ultraviolet.

Such is the science of gemology. By taking enough measurements, I can start with a list of hundreds of possible minerals and, hopefully, systematically eliminate possibilities down to one.

There is a point where identifying gems becomes an art. The final determination is made by human observation, combined with knowledge and experience, rather than measurements taken with precision instruments. This is especially true when it comes to separating natural from synthetic gems. The measurable physical and optical properties of a synthetic ruby will be identical to those of its natural counterpart. Distinguishing natural and synthetic stones involves observing inclusions in gems through a microscope. In some cases, this is simple and straightforward. In other cases, this requires judgment based on experience. Microscopic details can be subtle!

Fluorescent Ruby - gem identification
Testing a gem’s reaction to ultraviolet light is one technique that can be used for gem identification. All rubies, both natural and synthetic, fluoresce under ultraviolet light. However, there are some slight differences in fluorescence between natural and synthetic rubies and even between stones sourced from different geographic locations. “Ruby (fluorescent),” Jegdalek, Saroby, Afghanistan. © Rob Lavinsky, www.iRocks.com. Used with permission.

A Little Gemology Is A Dangerous Thing: Learning More About Gem Identification

If you’re a novice gemologist, I hope you’ve learned two things from this brief introduction. First, the basic procedure for gem identification involves ascertaining a gem’s properties and narrowing your suspect list down to one. Second, and most importantly, a little knowledge can be a dangerous thing.

Learning gemology is a worthwhile endeavor. However, don’t make an expensive decision about a gemstone based on limited knowledge. Whether you’re a gemology student or a gemstone buyer, you should always be cautious about whom you trust for gem identification.

Most jewelers have limited experience with colored stones. If they have a Graduate Gemologist degree, that means they’re 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 outside the range of their experience and reference materials.

You can study gemology at a college or university. Of course, that will likely be very expensive and require a significant scheduling commitment. If you have the interest but not the time or the money, consider enrolling in the International Gem Society Certification Program. All the information you need is available online on the IGS website. You can proceed at your own pace without pressure and take the exams as often as you need. The program is also inexpensive.

cut ruby - gem identification
“Cut Ruby,” oval-cut, 1.41 cts, by Bkell. Public domain.