Classifying Gems

There are any number of ways by which gems can be classified. The remainder of this presentation describes several of the most common ways:

· PRECIOUS OR SEMIPRECIOUS: (HISTORICAL VIEW OF VALUE)

· FACETED OR CABOCHON: (CUTTING STYLE)

· NATURAL OR SYNTHETIC: (ORIGIN)

· ENHANCED OR UNENHANCED: (TREATMENT STATUS)

· SIMULANT OR FAKE: ( HOW REPRESENTED)

· COLORED STONE OR DIAMOND: (GEM INDUSTRY VIEW)

· JEWELRY OR COLLECTOR GEM: (WHO WILL BE THE END USER)

Classified By Historical View of Value: "Precious or Semiprecious". 

These terms were routinely used (until about the 1980's) to separate diamond, ruby, sapphire, emerald and sometimes pearl, from all other gem species such as tourmaline, jasper and amber. Most gemologists no longer use these words and consider them out-moded. Why?

The term, "precious", implies rarity and high value, but, in reality, the individual specimens of each gem species and variety exist within in a full spectrum of rarity, and of value, from very low to very high. Some pieces of "semiprecious" gems are rarer, and more valuable than some individual specimens of "precious" gems.

 

[Precious? ruby (in zoisite) worth about $1-$2/ct -- semiprecious?

So what should we call them then? Simple: ----> gemstones or gems<-----. These terms will cover them all, regardless of where a given piece lies within the continuum of rarity, beauty, and value for its species.

So seriously is this idea taken that the "Code of Ethics and Principles of Fair Business Practices" of the American Gem Trade Association (a colored stone trade organization) instructs members to "avoid the use of the term "semiprecious"in describing gemstones", and they have purgedthat term from all their publications.

Classified By Cutting Style: Faceted or cabochon cut:

 They are the two most common ways in which gems are fashioned.

Faceted stones are usually cut from transparent rough of relatively high clarity. They are fashioned with a top (crown) and a bottom (pavilion) that have intersecting flat planes called facets, on their surfaces. These facets have shapes that are generally triangular, kite shaped or rectangular.

Cabochon ['kæbəʃɔn] cutting is most often used for translucent and opaque gems and such pieces generally have a flat bottom and a smoothly curved top called a dome.

 

[Faceted peridot, cabochon cut lapis lazuli] 

The parts of a faceted gem:,

 

Girdle: The girdle is the divider between the top and bottom of the gem. It defines the face-up outline, and the maximum dimensions of a faceted gem. In well proportioned stones, it usually comprises about 2% of the total depth of the gem.