A detective often needs multiple breaks in the case to find out “who dunnit.” A Gemologist does too. Last week, www.angelacisneros.com/post/csi-gemology-part-3 we talked about how the Refractometer can help narrow down the list of suspects or possibilities the gemstone could be. One of the key tests to determine what a gemstone is has to do with whether it is singly refractive (SR), doubly refractive (DR), or aggregate (AGG), and the Polariscope is the tool a Graduate Gemologist uses to discover that information. It is a desk-top tool that has two polaroid plates and a light source and is fun to explore with!
When you definitively find out how the gemstone refracts light, it narrows down the possibilities even more. For example, synthetic Moissanite looks similar to a diamond, but a diamond is singly refractive while Moissanite is doubly refractive. What do I mean when I talk about singly and doubly refractive? Let’s take this back to Physics class!
· Singly Refractive (SR): When a beam of light enters the gemstone, it does not split and remains a single beam as it exits the gemstone.
· Doubly Refractive (DR): When a beam of light enters the gemstone, it splits and becomes two beams of light as it exits the gemstone.
· Aggregate (AGG): An aggregate gemstone has thousands of microscopic crystals instead of being one single crystal. Some gemstones that are aggregate are Jasper, Agate, Nephrite, and Jadeite.
Another use of the Polariscope with a conoscope (a small, glass sphere that has no strain) is to find a gemstone’s optic figure. When a gemstone is doubly refractive, the light breaks up into multiple beams that travel in different directions throughout the gemstone. Gemstones will have distinctive patterns that you can see using the Polariscope. For example, a bull’s-eye optical figure is only seen in quartz and synthetic quartz. Usually, finding an optic figure is not a main test that is used, but sometimes, the tools don’t always give a clear answer, and Gemologist needs more information to make a call.
As you can see, properly identifying a gemstone has many steps and many fun tools! I realize that the tools and terms can be a bit confusing. It took me years of study and practice to understand much of what I have been sharing with you. If you have any questions, please feel free to contact me, and I’d love to discuss! If I don’t know the answer, I will find out for you!
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Photo Credit: @karlijean_