How to Test Gems

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Testing gems to identify them is a relatively simple, quick process. You need to be very gentle in performing the tests, however, to prevent damage to the gems. A hardness test is one of several tests and observations that can be performed to help identify a gemstone. Another test is the refractive index test. You can also make observations such as checking the gem's look in natural and incandescent light to see if it changes color.

Things You'll Need

  • Fine steel file
  • Gemstones
  • Refractometer
  • Polariscope
  • Loupe
  • Microscope
  • Overhead lamp
  • Obtain a fine file. Gently move the gemstone on the file's surface. If the stone has a hardness of seven or more, there will not be much damage to the gem from the file. It should glide along the file's surface. If it catches at all on the file, then the gem's hardness is less than seven and it may be an indication that the gemstone is not real. Be careful in your determination, however, since gemstones like lapis lazuli, moonstone and amazonite have a hardness of six or less.

  • Test gems by other procedures to help identify them. To do this clean the gemstone using an artist's brush. Use a loupe and overhead lamp to examine the gem. A loupe is a small magnifying lens used by watchmakers and jewelers. It can fit into the eye socket or may also be held in the hand. Using this lens will better allow you to see inclusions, which are solids, liquids or gas trapped in the mineral.

  • Note the color, cut, any inclusions, and the physical qualities of the gem, including detailed information on any fractures and chips you see. Use a microscope to look at the inclusions in the stone. Look at the fractures to determine if they are conchoidal, meaning the fracture has a smooth shell-shaped concave or convex surface.

    Check for a color change by looking at the gem under natural light and incandescent light, or white light like that from a light bulb.

  • Check the refractive index by placing the gem on the appropriate place on a refractometer. Get a reading from the long and short axis if the stone is rectangular.

  • Use a polariscope if you think a gem is singly refractive, meaning that light passes through it only once. If a gem is doubly refractive then the light that passes through it will be divided, going in different directions. Write down the gemstone's refractive index or indices.

  • Place all the information you have gathered into a computer program call Gemology Tools and see what gem you have. Gem identifying technology is also available at the Gem Society website – simply type in your readings and observations to determine what gem you have.

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References

  • Photo Credit garnet gem image by OMKAR A.V from Fotolia.com
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