A Guide to Gem-Related Terminology Part 1: Describing a Finished Gemstone

While chatting with the lovely dragons/dragonlings, I realized just how many common gem terms get misused or are poorly defined even with a skilled Google search. This has inspired what I hope will be an informative (but not too horribly dry and boring) series of educational articles that will go over the terminology of different aspects of the gem and jewelry industry. Up first on the dop? Finished gemstones and the many terms we use to describe them.

Anatomy of a faceted gemstone

Of course, as we well know with precision-cut stones, there are an infinite number of ways a gem can be fashioned. For the sake of brevity (and my sanity), I'll be focusing on the most common cutting styles. The standard faceted gemstone can be roughly divided into three primary sections: the crown, girdle and pavilion.

Crown

The "crown" is the top portion of the gem that is usually visible when it is set in jewelry. It will often feature a single large, raised central facet called the "table." In standard brilliant cuts, this table is framed by triangle-shaped facets known as "star" facets and kite-shaped facets known as "bezel" facets (not to be confused with the bezel style of setting, which I am saving for a future post on jewelry styles), and the triangular facets that are on the outside edge of the crown are the "upper halves."

For step-cut stones the table is instead surrounded by a series of graduated four-sided (and occasionally 3-sided at the corners corners) facets, generally referred to as simply "crown facets." I have no idea why they don't deserve their own special, fancy names and I agree it is totally unfair. Because I'm sure that is exactly what you were thinking just now.

Sometimes the crown does not feature a table, but instead has a series of facets throughout. A rose cut, for example, is made up of a pattern of triangular or diamond-shaped facets that come to a point in the center of the crown. Another popular cutting style without a table is the checkerboard cut, where the repeating square facets resemble the spaces on a checkerboard. Meanwhile, in a portrait or tablet cut stone the crown and pavilion might be completely interchangeable, with both sides featuring what amounts to a gigantic table facet framed by smaller facet details.

Girdle

The "girdle" is the (usually) thin separating layer between the crown and pavilion. Although it is often overlooked, this part of a faceted gem is more important than you might expect. The condition and thickness of the girdle can not only affect the appearance of a gemstone, but it can also impact its durability and ability to be set. If a girdle is too thin, it is more prone to damage; an overly-thick or uneven girdle might prevent your stone from fitting in a standard setting properly.

Girdles can be unfinished, polished, faceted, or bruted (this last one only applies to diamonds, as it refers to part of the initial shaping phase of diamond faceting where two rough diamonds are ground together to create the outline of the girdle).

Pavilion

Last but certainly not least is the pavilion, which refers to the portion of a faceted gemstone that sits below the girdle. For standard brilliant cuts, a pavilion is usually made up of elongated kite facets called "mains" and elongated triangular facets called "lower halves." And, you guessed it, in step cuts the pavilion facets are simply, well, "pavilion facets." Traditional rose cuts will often have a flat base, but more modern interpretations of the style may have brilliant, step, or a completely unique style of pavilion.

Culet/Keel

Technically the culet or keel are part of the pavilion, but I think they deserve their own special mention. A "culet" is a (usually) small facet on the bottom of a faceted gem where the pavilion comes to a point, like with round, pear, heart, and triangular cutting styles. This additional facet is not always present, but is often used to protect the delicate point from damage. Older cuts like Old Mine and Old European faceting styles feature a characteristically prominent culet, sometimes more noticeably than others.

In some styles of elongated cuts like the marquise or emerald shapes, the pavilion facets don't come to a single point. Instead, they meet at an extended line at the bottom of the stone called a "keel" - a reference to its resemblance to the keel of a ship. The keel may also be faceted to create a culet.

Fancy Cut Terminology

In addition to terms outlined above, "fancy" (i.e. non-standard round brilliant) faceted cutting styles have their own special lingo. I find this is best conveyed with a diagram, so I've included the most common shapes that I've encountered below.

Pear

Marquise

Heart

Non-Faceted Gemstone Styles

Not every gemstone is best suited for faceting. Heavily included or especially soft gems, for example, may be too fragile for the faceting process. Faceting might also not be the best way to showcase a particular gemstone. Phenomenal materials like star sapphire and black opal often perform better when they have a rounded top, and opaque or translucent gems won't benefit much from faceting's increased light performance.

Cabochon

A "cabochon" or "cab" is a finished gemstone with a flat bottom and a smooth rounded top or dome. Lacking the facets to bounce around light within the gem, a cabochon cut nonetheless has its benefits. The dome provides the perfect surface for asterism (star patterns) and chatoyancy (sometimes referred to as a cat's eye), allowing the light reflecting off of their needle and tube inclusions to form striking bands on top of the stone. The relative simplicity of the cabochon style also makes it ideal for less expensive and softer gemstones that are heavily included or cannot take a high polish.

In some cases, a cabochon consists of more than one material stuck together. Due to its softness and tendency to crack or craze in heat, opals are commonly assembled in doublet or triplet cabochons to protect a small sliver of precious opal between harder materials like quartz and chalcedony.

Cameo

No, I'm not referring to a brief appearance in a popular television show. In this context, "cameo" refers to a gem with a raised carving. They might feature a comely lass, a Greek mythological figure, a bouquet of flowers...or pretty much anything. Although shell and coral cameos are quite popular (as are their plastic counterparts), I love when a carver utilizes the different layers of color in a banded hardstone like sardonyx to create a beautiful work of art.

Intaglio

Basically, an "intaglio" is the reverse image of a cameo. While a cameo features a raised image, an intaglio is recessed into the gemstone. This was handy back in the day for personal seals (the stamping kind, not the aquatic kind), as they were important marks of status and often highly intricate in order to prevent duplication.

Is that all?

I could write a full-length textbook on the various faceting styles and terminology, but I think that would exceed the Reddit word limit so I'm going to stop here. In future installments, I do plan on covering terminology on jewelry, clarity features, and the most commonly misused terms in the industry. Comment below if there is a particular word used by the biz that baffles or frustrates you, or something you'd like me to include in future posts!