Gemstone Examination Lesson


Step 3: Practical Gemology

Lesson 28

While preparing this lesson in gemstone examination, I was in the process of professionally identifying the following stones. Rather than create fictional examples, I decided to use the photos and descriptions of these actual gems and real-life cases to illustrate the procedures and problems you’ll encounter as a fledgling gemologist.

Gemstone Examination: Example 1

This stone looks like a tourmaline. I made that initial assessment based partly on its shape – tourmaline crystals are elongated, so rectangular gems are common – and partly on its color – green, but slightly grayish. It’s certainly not an emerald or other chromium-colored gem.

With the loupe, I saw that it’s well cut. It had some fingerprints and fractures, but no identifying inclusions.

The end facets are black. No light was passing through them. This is called a “closed C axis” and is common to tourmaline, but little else. For our purposes, we’ll simply note that the stone has strong pleochroism.

Next I took a basic refractive index (RI) reading. On the long axis it measured 1.643. Turning it sideways, it read 1.641. I put the stone in the polariscope

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