Naming Gems

Similarly to the way organisms are named in biology, in gemology, each distinct type of gem has a species name.

Species: A gem species is a mineral that has a definite chemical formula, and has a particular three dimensional structure. In regards to that structure, gems can have a crystalline (highly regular and organized), or amorphous (less organized) structure.

An example of a gem species is quartz. All quartzes, whatever their other characteristics, share the same chemical formula: SiO2 and are members of the hexagonal crystal system. (We'll be looking at the characteristics of the various crystal systems in a later lesson). The species "quartz" encompasses many quite different looking gems, though, from amethyst and citrine, to agate and jasper, to rutilated quartz and tiger'seye.

Another example of a gem species is corundum (commonly known as sapphire). All corundum gems share the chemical formula: Al2O3 and are members of the trigonal crystal system. 

Variety: A gem variety is composed of a sub-group, within the species, that shares distinct and notable characteristics, such as color, degree of transparency, inclusions, or optical phenomena with others of its kind. Not every gem species has multiple varieties, for example, there are no separate varieties within the gem species peridot.

Quartz Gems: 

[Species quartz: Varieties: amethyst, agate]

Amethyst is transparent, crystalline, purple quartz. Agate is translucent, usually banded or patterned, cryptocrystalline (made of ultra-microscopic crystals in an aggregate) quartz. Amethysts come in a range of purple colors from very light to dark, and agates come in a nearly infinite array of colors and patterns.

Corundum Gems: 

[Species corundum: Varieties: ruby, yellow sapphire, star sapphire]

Ruby is the variety name for red corundum, yellow sapphire is yellow corundum and star sapphire is translucent to opaque corundum that shows the optical phenomenon of asterism (forms a star figure from reflected light). The only variety of corundum that is simply called "sapphire" without any modifier is blue sapphire, all other colors have their own variety name (like ruby) or use a modifier like star, yellow, pink, white, etc.

Groups: In some cases, a number of closely related mineral species are placed into a larger, more inclusive category, called a mineral group. Examples are the garnet group and the feldspar group.

The individual species of the group share membership in the same crystal system, but although the chemical formulas amongst group members are very similar, they are not exactly the same throughout the group. Typically, the formulas gradually change by substitution of a set of chemical elements from one end of a continuum to the other.

Garnet Group: All garnets, whatever their individual species and varietal designations, are members of the isometric crystal system and are metallic silicate minerals with various proportions of Ca, Fe, Mg, Al, Cr and Mn substituting for each other within a similar chemical formula.

(To amplify: the generic formula for any garnet is A 3B 2Si 3O12 where the "A" position can be occupied by iron, calcium, manganese or magnesium, and the "B" position can be occupied by aluminum, iron, titanium or chromium. The rest of the formula is standard for all gems known as garnets).

Garnet Group Gems:

[Group: garnet, Species: Spessartite锰铝磂石, Group: garnet, Species: grossularite钙铝榴石, variety: Tsavorite]

The orange oval stone above belongs to the Spessartite* species within the garnet group. (Spessartites are manganese rich), and no individual varieties are designated within this species. The green stones above belong to the calcium rich grossularite species within the garnet group. There are several named varieties of grossularites, including medium to dark green stones colored by trace amounts of chromium and vanadium, called Tsavorite.

*When species or variety names come from proper nouns such as those designating a person (like Kunzite, named for G. F. Kunz, or Spessartite, named after the type location, Spessart in Germany), they are capitalized. Otherwise lower case is used, as in grossularite, agate and amethyst.

Trade Names and Misnomers误命名:

In addition to the official names given to gems, there are also a multitude of trade names, brand names, and misnomers that are in use. In fact, just as happened in the history of biology, the confusion over which mineral or gem was called what, where, by whom, has led to the development of a rigorous system for international naming of minerals and gems. Although this formal system is used by professionals, students, and serious gem enthusiasts among the public, many other names are still in use and can create confusion.

 

Trade Names:

In modern times, trade names have most often developed when a new gem material is first discovered and marketed, as a way to "romance the stone". Let's say you are in Tanzania and you mine a facetable, but insipid looking light brown, transparent form of the mineral zoisite. You discover that heat treating will turn it to a gorgeous blue-violet color. The correct descriptive term would be: heated brown zoisite.

Who would rush out to buy that? But, what if you call this gem something exotic and evocative of its foreign mine site, like "Tanzanite"--> now you something more marketable!

[Heated brown zoisite = Tanzanite]

Sometimes, what starts out as a trade name becomes so widely used that it is essentially adopted as the official name. Exactly this has happened in the case of Tanzanite.

Other examples of names which started out as marketing ploys策划 and ended up on the officially sanctioned list include: "Kunzite" for pink spodumene锂辉石, named for the famous early 20th century gem explorer and writer, G. F. Kunz and, "Tsavorite" for green grossular garnet named for its original mine locale (Tsavo National Park in Kenya).

[Kunzite, Tsavorite]

This strategy doesn't always work, and intended trade names sometimes fail. There are numerous examples in which trade names were used for a period of time, or by a specific seller, but then either died out, or never became widespread. An aggressive campaign to present heated blue zircon as "Starlite" failed, as did a similar effort to label high grade sugilite苏纪石 as "Royal Azel".