Glossary of Terms

Carat

The unit of weight by which diamonds and gemstones are measured. One carat equals 200 milligrams, or 1/5 of a gram. The word comes from the carob bean, whose relatively consistent weight was used in ancient times to measure gemstones or precious metals. 

Culet

The bottom point of a brilliant cut diamond or faceted gemstone.  It is often blunted, especially with diamonds.  The bottom of step cut gemstones (emerald cuts) is called a keel.

Crown

The top part of the diamond above the girdle.

Depth

The height of a diamond from the table to the culet. The depth is described as a percentage of the diameter of a round diamond or percentage of the width of the fancy shape diamonds.

Diamond

Virtually pure carbon atoms crystalized by high heat and pressure in a cubic pattern to form the hardest substance known to mankind.  Diamonds are produced at depths between 100 and 200 miles deep, one of only two gems which form in the Earth's mantle, rather than the crust.  They are also the only major gemstone made up of only one element.

Dispersion

Arranged around the table facet on the crown are several smaller facets (star, bezel and upper girdle facets) angled downward to the girdle.  These facets are designed to break up white light as it exits the diamond by separating it into the full range of spectral colors and is called the diamond's fire or dispersion.   Cutting the bezel facets (the kite shapes) to an angle close to 34.5 degrees and cutting the table facet to between 53% and 58% of the diamonds diameter will maximize dispersion.

Facet

The smooth, flat faces on the surface of a diamond or gemstone. They allow light to both enter a diamond and reflect off its surface at different angles, creating the wonderful play of color and light for which diamonds are famous. A brilliant cut of any shape has 58 facets (or 57 if there is no culet). The shape, quantity, and arrangement of these facets may differ slightly among the fancy shapes. 

Finish

The term "finish" covers every aspect of a diamond's appearance that is not a result of the diamond's inherent nature when it comes out of the ground. The execution of the diamond's design, the precision of its cutting details, and the quality of its polish are all a consideration when a gemologist is grading finish. When examining a diamond's grading report, one will see its finish graded according to two separate categories: polish and symmetry.

Fluorescence

A reaction to longwave or shortwave ultraviolet light causing a gemstone to appear as a different color.  This effect is observed in approximately 35% of gem-quality diamonds when exposed to LW UV (black light) as a soft-colored glow (97% are bluish violet but other colors are possible).  In most lighting conditions fluorescence is usually not detectable to the naked eye but it can make a slightly tinted diamond appear one or two grades whiter.

Gemstone

Defined as a crystal, mineral or organic substance used for jewelry which possesses beauty, rarity and durability.   Some gems may have only two of these qualities.

GIA

Founded in 1931 by Robert Shipley, Jr. this non-profit organization upholds the highest standards for grading diamonds and other precious gems. The GIA has many of the most respected and well regarded gemological laboratories in the world; GIA was responsible for developing and standardizing the diamond grading system that is used today by nearly all other gem labs and jewelers throughout the world.

Girdle

The outer edge, or outline, of the gemstone shape between the crown and the pavilion. The girdle is not graded but is described by its appearance at its thinnest and thickest points and it's finish such as frosted, polished or faceted.  For diamonds the descriptions of girdle thickness ranges as:  extremely thin; thin; medium; slightly thick; thick; or extremely thick. While it is less desirable for a round diamond to display an extremely thin or extremely thick girdle, such girdle widths are more common and acceptable in fancy shape diamonds.

Inclusion

A clarity characteristic found within a diamond or other gemstone which were created when the gem first formed in the earth or during movement to the surface.  They can be described as feathers (breaks in the grain), crystals, pinpoints or clouds (groups of pinpoints).  Many inclusions are smaller crystals of the host rock any of numerous other minerals that were incorporated during gem formation.

Karat

A description of gold purity describing how much weight out of 24 parts is gold.  For example, 14 karat gold is 14/24 (or 58.5%) gold.  Other metals such as copper, nickel, zinc and silver are mixed with gold to make it more durable and affordable and will also determine the color of the gold.  In the United States, gold is most often alloyed to 10 karat, 14 karat or 18 karat.  

Pavilion

The lower portion of the diamond or faceted gemstone below the girdle.

Symmetry

Refers to variations in a diamond's overall shape. The small variations can include poorly shaped facets, facets that fail to point correctly or a misalignment between the crown and pavilion at the girdle (all of which are entirely undetectable to the naked eye). Symmetry is regarded as an indicator of the quality of a diamond's cut; it is graded as either Excellent, Very Good, Good, Fair or Poor.

Table

The usually octagon shaped flat facet centered on the top of a diamond or gemstone; it is also the largest facet.