gem identification quiz - green gem

Peridot, emerald, or something else? This quiz can help beginner gemologists learn how to choose identification tests and run them efficiently.

New gemology students often fuss over inconsequential data when identifying gems for the first time. In the process, they miss important clues. Getting practical experience is vital. In order to help make the transition from the textbook to the real world, I’ve created a gem identification quiz series. These “What is it?” quizzes are designed to be as realistic as possible. Hopefully, they’ll give student gemologists a better idea of how to proceed based on the information at hand. In this manner, they’ll learn not only the process but also time saving shortcuts.

You’ll find the first gem identification quiz below. The rest of the series is available to those enrolled in the International Gem Society (IGS) Professional Gemologist certification course.

Gem Identification Quiz #1: A Green Stone

A customer brings you a green, transparent stone (shown above) and wants to know if it’s an emerald or a peridot. Peridot is her birthstone, but she know emeralds are much more valuable! With fingers crossed, you begin your examination.

Loupe Exam

First, clean the gem and examine it with a 10X loupe. You find a small feather and note the stone is very well cut, but nothing more.

Microscope Exam

Next, take the stone to your microscope and examine it thoroughly with dark field and oblique illumination. You see it has a small conchoidal fracture with vitreous luster on the culet. However, you don’t find any additional inclusions.

Refractometer Exam

Use your refractometer to take a basic refractive index (RI) reading. (Two readings at 90° to each other). You note your readings: 1.621 and 1.627.

Polariscope Exam

A quick check with a polariscope shows that the stone is doubly refractive. However, you can’t find an optic sign. While examining the stone, you notice that it’s at least moderately pleochroic with yellowish green/green colors

Review What You’ve Found

I chose these initial tests because they’re the easiest and least time consuming. Look at what you learned about your gem in just a few minutes: the approximate RI range, double refraction, and moderate pleochroism.

Of the other clues you’ve found, the feather and the conchoidal fracture with vitreous luster are of least importance. Unfortunately, these are so common they have little identification value.

Slightly more important, you know the stone is green and transparent. Yes, dozens of stones possess these qualities. Nevertheless, they still limit the possibilities a bit. For example, you can eliminate malachite, turquoise, and opal. Usually, being well cut indicates a valuable gem. Few people would spend much time on a synthetic. However, this proves nothing. Just keep this clue in mind. It may be important later.

Take the Gem Identification Quiz

After these initial tests, consult your reference materials and try to narrow down the options for your gem’s identity. Now, answer the following questions:

Question 1

At this point, what do you think the stone most likely is?

Question 2

What test or tests would you run next?

Gem Identification Quiz Answers

Question 1

The answer depends on your reference materials and what data you choose to search for. If you have the Gemology Tools software, the answer is easy. In this program, enter the information you have.

  • Color: green.
  • Optic Character: DR.
  • RI high and low: 1.621 and 1.627. (Note, use what you measured. The actual range may be greater).
  • Pleochroism: 2 colors and moderate.
  • Transparency: transparent.

The search results will list actinolite, topaz, and a few varieties of tourmaline as possibilities. You don’t need to identify the tourmaline variety at this point. Therefore, you need a test or tests to distinguish actinolite, topaz, and tourmaline.

Question 2

Topaz has a significantly different specific gravity (SG) than the other possibilities. However, SG won’t distinguish actinolite from tourmaline. Each of these gems has a different optic sign. So, that’s the deciding factor. Since you couldn’t find the optic sign with your polariscope, try your refractomer, instead. When you’ve determined the optic sign, you can make a positive identification.

Gem Identification Quiz Follow Up

Hopefully, this little lesson helps you understand the gem identification process. Gather your initial data, review your findings, consult your references, eliminate possibilities, and choose additional tests.

So, what is that green gem? That depends on its optic sign. I haven’t revealed the answer. The quiz is designed to help you learn to winnow data and pick appropriate tests.

However, here’s a little more information about one of the possibilities.

Typically, you can easily identify tourmalines. Strong pleochroism is a good indicator, especially if you see two entirely different colors, like orange and green. Another quick way to identify tourmalines is finding hollow growth tubes. Either of these qualities indicate you’re likely looking at a tourmaline. Next, check the RI. If it matches tourmaline, the only other thing you need for proof of identity is the optic sign. No other gem has strong pleochroism, the same RI, and optic sign as tourmaline.

Tourmalines frequently have stress, which should make finding the optic sign in the polariscope easy. However, even if you don’t find it with that tool, you can still use your refractometer.

If you’re an IGS member, take a look at the entire quiz series.