Gemstone Classification

I’ve always preferred to work in strictly metal, rather than incorporating a lot of gemstones. As my skills grow through my apprentice program, however, I am beginning to incorporate more stones. On a side note, however, you still won’t see me working with tons of color, but mostly diamonds with some other accents. Those who know me well, know that, while I appreciate the gorgeous colors of these stones, I’m a bit color-phobic.

As I begin to use more gemstones in my work, I thought this was a good time to explain some of the different classifications of stones and some of the terms you might see. This is a huge topic, and one that there are entire courses of study on. I hope to give you just a brief overview so some of the terms you will encounter will make more sense.

Precious vs Semi-Precious

The first thing you might hear about a gemstone is precious vs semi-precious. The International Gem Society states that this term is not really valid anymore since many of the semi-precious stones are actually quite a bit more expensive than precious stones and there are so many exceptions to these categories that they really don’t mean much anymore. Traditionally, however, diamonds, rubies, sapphires and emeralds are considered precious stones. All other gemstones are considered semi-precious. For example, alexandrite, agate, amethyst, aquamarine, garnet, lapis lazuli, moonstone, opal, pearl, peridot, rose quartz, spinel, tanzanite, tourmaline, turquoise and zircon are all semi-precious stones.

Natural Stones

Natural stones are just that, stones that have been mined from the earth. Many stones require some enhancement to either stabilize them or to bring out the colors. Even though these stones have been treated, they are still natural stones. Some of the common treatments are:

• Bleaching - A chemical is used to alter and/or reduce a component of, or the entire color, of a porous gem. Often used with jade and pearls, and sometimes with coral, calcedony and tiger’s eye quartz.

• Surface Coating - A coloring agent like paint or metal oxides is applied to the back surfaces of gems (a treatment known as “backing”), or paint applied as a coating to all or a portion of a gemstone’s surface with the effect of altering the color. Sometimes used on diamonds, topaz, coral, pearls, and quartz. Special care needs to be taken with these stones.

• Dying - Colored dyes are introduced into porous or fractured gems to change their color. Often used on colored pearls and sometimes in a range of other stones including coral, turquoise, lapis lazuli, howlite, nephrite jade, chalcedony, quartz, emerald, and ruby.

• Fracture or Cavity Filling - Fractures in a gemstone are filled with a glass, resin, wax or oil to conceal their visibility and to improve the apparent clarity, appearance, and stability. Most commonly found in diamonds, rubies, sapphires, and emeralds, but can be found in other stones as well.

• Heat-Treated - A gem is exposed to high temperatures for the purpose of altering its color and/or clarity. This is one of the more common treatments, and is often found in amber, amethyst, aquamarine, citrine, ruby, sapphire, tanzanite, topaz, tourmaline, and zircon.

• • High Pressure, High Temperature (HPHT) Treatment - Heating a diamond to high temperatures under high confining pressures to remove, or change its color. Used sometimes for colorless diamonds, but more often for colored diamonds.

  • Impregnation - The surface of a porous gemstone is permeated with a polymer, wax or plastic to give it greater durability and improve its appearance. Commonly seen in turquoise, lapis lazuli, jadeite, nephrite, amazonite, rhodochrosite and serpentine.

  • Irridiation - Exposure of a gem to an artificial source of radiation to change its color. Often used with topaz and fancy colored diamonds, but can also be seen with beryl, quartz, ruby and sapphire.

  • Laser Drilling - A narrow focused beam of laser light to burn an open channel from the surface of a diamond to reach dark inclusions. Sometimes used on diamonds.

  • Lattice Diffusion - Penetration of certain elements into the atomic lattice of a gemstone during heat treatment, with the goal of changing or accentuating its color. Seen in ruby, sapphire, and labradorite.

  Synthetic Stones

  You might hear different terms such as synthetic, artificial, lab-grown, lab-made, man-made, etc., but all of these terms refer to something that was create in a lab rather than in nature. A synthetic stone may simply appear to be the same as a natural stone, but some actually have the same chemical structure as a natural stone, with the same inclusions and flaws. While these latter stones are “real” stones, they are not natural stones. So, when you see the term “synthetic,” it means a stone that has been created to look like a natural stone. When you see the term “lab-grown,” it means that is a “real” stone that has been created in a laboratory instead of naturally in the earth. There is a great article you can read here.

  Cubic zirconia is a great example of a synthetic stone that might appear to look like a real stone, but is not chemically identical. Moissanite is another example of a lab-created stone that looks like a diamond but is not chemically identical. On the other hand, there are lab-grown diamonds which are chemically identical to the natural diamond. These are becoming a popular option since there are so many concerns about the ethics of sourcing natural diamonds.

  Gemstone Ratings

  This is a huge topic, so I’m only going to briefly touch on this subject. You can find more information here. Basically, a gemstone is rated on four qualities: color, clarity, cut and carat. Once these 4 C’s have been evaluated, the gemstone is given a “grade.”

  For colored gemstones, this grade ranges from D (lots of inclusions, not transparent, mostly suitable for cabochons) up to an AAA rating, which is an excellent gemstone. If a stone has an A rating, it means that it is a good quality gemstone - it is well cut, has a good transparency and lets light through, and has few inclusions. As more A’s are added to this rating, obviously these qualities are even more exceptional.

  Diamonds are rated separately using these four qualities. To find more information about this rating system, please see this page.