Gemstone Guide | National Rarities | Leading Gold & Estate Buyer
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Gemstone Guide

Buying a gemstone is different from buying a diamond in many respects. While a gemstone is still evaluated by the same 4C’s as diamonds are in terms of cut, color, clarity and carats, each is judged separately. That is, sapphires are only compared to other sapphires and not emeralds and rubies, for instance. In the following gemstone guide, we’ll uncover some of the different ways gems are evaluated. The more you know about how gemstones are judged, the more confident you can be in making choices about your gemstone jewelry.


Gemstones come in a number of different shapes, from radiant round to elegant emerald. Here are just a few examples. 


Gemstones are judged by a range of color running from light to dark and more vivid to less vivid. Only a small scope of that color is considered preferable. Below, you can see that the entire spectrum is represented by different types of gems. 

  • Red: Ruby, Mozambique Garnet
  • Pink: Pink Sapphire, Rhodolite Garnet  
  • Yellow: Yellow Sapphire, Citrine
  • Green: Emerald, Bloodstone, Jade, Peridot
  • Blue: Blue Sapphire, Aquamarine, Blue Chalcedony, Blue Spinel, Blue Zircon, Lapis
  • Purple: Amethyst, Tanzanite
  • White: Akoya Pearl, Freshwater Pearl, Mabe Pearl, South Sea Pearl, White Spinel, White Topaz, Moissanite, Opal
  • Brown: Smoky Quartz
  • Black/Gray: Tahitian Pearl, Onyx


Gems are cut in a variety of ways. Transparent stones are faceted in order to maximize their color. Other stones, such as jade, opal and onyx, are cut into a smooth, domed shape known as a cabochon. And still other stones like cameos are intricately carved.


Naturally occurring characteristics, known as blemishes and inclusions, are part of most gemstones. Blemishes occur on the outside of the stone while inclusions are on the inside. Some stones are known for having more inclusions than others, such as emerald, while others have few inclusions, like citrine. Thus, each stone will be graded for clarity differently and according to its type. 


Like diamonds, gemstones are measured using carats. A carat is a measure of weight equivalent to 0.2 grams or 0.007. One carat weighs about as much as a single paperclip. Yet, unlike diamonds, each gemstone has a different density, which determines its weight versus its measured size. A one carat citrine won’t measure the same as a one carat sapphire, for instance.

Gemstone Enhancement

Many gemstones are treated through a number of processes other than cutting or polishing to enhance their appearance, durability or availability. The following gemstone enhancement codes were originally published by the American Gem Trade Association. 

N: The “N” symbol appears on the chart only for natural stones which are not currently known to be enhanced. 

E: The “E” symbol indicates that a gemstone has undergone its traditional enhancement process.