The IGI glossary page provides definitions for various terms commonly encountered in the diamond and gemstone industry. These terms are relevant to both consumers and professionals in the field. The glossary covers a wide range, including:
- Diamond grading terminology: terms like “Carat Weight,” “Clarity,” “Cut,” and “Color” (the 4Cs) are defined.
- Gemstone characteristics: definitions cover aspects like “Fluorescence,” “Fracture,” and “Inclusion”.
- Jewelry components: terms like “Girdle” and “Facet” are explained.
- Company information: “IGI” itself is defined, explaining its role as a diamond and gemstone grading laboratory.
This glossary serves as a helpful resource for anyone seeking to understand the terminology used when discussing diamonds, gemstones, and jewelry.
Glossary of Abbreviations
| APPROX |
Approximate |
| AS |
Appraisal Summary |
| BAG |
Baguette |
| BGIA |
Based on GIA Report # |
| BSGIA |
Based Solely on GIA Report # |
| C |
Colorless |
| CT |
Carat Weight |
| CBGIA |
Color Based on GIA Report # |
| CCBGIA |
Color and Clarity Based on GIA Report # |
| CCGEAAM |
Color and Clarity Grade Expressed as a Minimum |
| CCGPTM |
Color & Clarity Graded Prior to Mounting |
| CONT |
Containing |
| CDPBC |
Chain Description Purported By Client |
| CGIBOCTS |
Clarity Grade is Based On Cloud Throughout Stone |
| CGIBOIGL |
Clarity Grade is Based On Internal Grain Lines |
| CLA |
Clarity |
| CLGAAM |
Clarity Grade Expressed As a Minimum |
| COL |
Color |
| CSBAGS |
Center Stone Based on AGS Report # |
| CSBGIA |
Center Stone Based on GIA Report # |
| CSGPTM |
Center Stone Graded Prior to Mounting |
| CTS |
Cloud Throughout Stone |
| DWT |
Penny Weight |
| EM |
Emerald Cut |
| EST |
Estimated |
| EX |
Excellent |
| G |
Good |
| GAMP |
Graded As Mounting Permits |
| GGEAAA |
Gemstones Grade Expressed as a Average |
| GGEAAM |
Gemstones Grade Expressed as a Minimum |
| GLP |
Grain Lines Present |
| GPTM |
Graded Prior to Mounting |
| HI |
Heavily Included |
| IAC |
Inclusions Affect Color |
| IGLP |
Internal Grain Lines Present |
| ILDHP |
Internal Laser Drilling Present |
| INS |
Insurance |
| KT |
Precious Metal Content |
| LDHP |
Laser Drill Holes Present |
| LI |
Lightly Included |
| MCPBC |
Mounting Composition Purported by Client |
| MDPBC |
Mounting Description Purported by Client |
| MEAS |
Measurements |
| MED |
Medium |
| MI |
Moderately Included |
| MM |
Millimeters |
| MOD |
Modified |
| MQ |
Marquise Brilliant Cut |
| N |
Thin |
| NAT |
Natural |
| NC |
Near Colorless |
| NP |
Numerous Pinpoints |
| PLAT |
Platinum |
| POL |
Polish |
| PR |
Pear Shape Brilliant |
| PRE |
Pre-existing Inscription Present |
| PURP |
Purposes |
| RBC |
Round Brilliant Cut |
| REPL |
Replacement |
| RET |
Retail |
| RMB |
Rectangular Modified Brilliant |
| SBAG |
Straight Baguette Cut |
| SGL |
Surface Grain Lines |
| SGLP |
Surface Grain Lines Present |
| SMB |
Square Modified Brilliant |
| SSBGIA |
Side Stones Based on GIA Report # |
| SSGAMP |
Side Stones Graded as Mounting Permits |
| SYM |
Symmetry |
| TBAG |
Tapered Baguette Cut |
| TK |
Think |
| TOT |
Total |
| TP |
Transparent |
| TRI |
Triangular Modified Brilliant |
| TW |
Total Weight |
| VAL |
Value |
| VG |
Very Good |
| WG |
White Gold |
| WT |
Weight |
| YG |
Yellow Gold |
A written estimate of the approximate retail replacement value of the item described. They can be used for insurance purposes and should be updated every few years.
On a round brilliant diamond, these are eight large kite-shaped facets on the crown. Also called main crown facet.
Brilliance describes the reflections of white light coming from the diamond in “face-up” position. It is the effect that makes diamonds unique among all other gemstones. While other gemstones also display brilliance, none have the power to equal the extent of diamond's light-reflecting power. Brilliance is created primarily when light enters through the table, reaches the pavilion facets, and is then reflected back out through the table, where the light is most visible to your eye.
Round diamond with 57 facets (58 if there is a facet on the culet).
In this type of cutting shape, all facets appear to radiate out from the center of the diamond toward its outer edges. It is called a brilliant cut because it designed to maximize brilliance. Round diamonds, ovals, radiants, princesses, hearts, marquises, and pears all fall within this category of cut.
The standard unit of measurement of the weight of a diamond. One carat equals 1/5 of a gram or 1/142 of an ounce.
1 carat=100 points. The word Carat comes from the carob bean, whose consistent weight was used in times past to measure gemstones.
A type of inclusion consisting of a large or deep opening in the diamond.
The degree to which a diamond is free from internal characteristics and blemishes.
Clarity is graded on a scale from Flawless (FL) to Imperfect (I).
Any process used to improve the apparent clarity of a diamond. This may include filling fractures and cavities with
foreign substances such as glass or resin, depending on the stone.
A crack in a diamond which is parallel to one of its crystallographic planes. A cleavage may be caused by inherent internal strain or by a sharp blow. The crack usually extends to the surface.
A group of minute to very small, white inclusions which give a "cloudy" appearance.
A system of grading diamond colors based on their colorlessness (for white diamonds) or their spectral hue, depth of color and purity of color (for fancy color diamonds). For white diamonds, IGI uses the internationally recognized grading system which runs from D (totally colorless) to Z (light yellow).
The part of the diamond that is above the girdle. It consists of the table and the crown facets below it.
The angle measured between the girdle plane and the bezel facets. Along with the table size, the crown angle helps determine the amount of dispersion (also called "fire") displayed by the diamond.
The crown height is measured perpendicular to the girdle and is expressed as a percentage of the average girdle diameter.
A type of inclusion. A crystal is a mineral deposit trapped inside the diamond.
The point at the bottom of a full-cut diamond. Some diamonds have a faceted culet.
An antique style of cut that looks like a mix between an Old Mine Cut (see Mine Cut Diamond) and a modern oval cut.
The cut (or make) of a diamond refers both to the proportions and the finish of a polished diamond. The cut is the most important of the 4Cs (cut, color, clarity, carat) in determining the diamond’s overall beauty, and is the only man-made contribution to a diamond's beauty and value.
The distance between the table facet and the culet measured in millimeters.
Also called "total depth", this figure is expressed in % and is the result of the following calculation:
- Round-shaped diamond: the diamond’s depth divided by its average diameter.
- Fancy-shaped diamond: the diamond’s depth divided by its width.
This covers thin girdles as well as inclusions that weaken a gem.
A term used in clarity-grading: "eye-clean" diamonds should have no inclusions that are visible through the table to the unaided eye.
A polished plane on the surface of a gemstone.
Diamonds having color more intense than "Z", as well as diamonds exhibiting color other than yellow or brown are considered fancy colored diamonds. These diamonds are graded using separate systems which indicate the characteristics of the color, and not just its presence.
Any diamond shape other than round.
A fracture or break in a diamond that looks like a white feather.
The property in approximately 50% of all diamonds that makes them glow when exposed to ultraviolet light (such as the lighting frequently seen in night clubs). Diamonds can fluoresce in a number of colors, but blue fluorescence is most common. Depending on its intensity, blue fluorescence may enhance the color of some diamonds by hiding their yellow tint.
A chip or break on a diamond that is not in the direction of a cleavage plane
A treatment whereby feathers in a diamond are filled with an artificial substance. This treatment is not permanent since the filler can dissolve and escape over time.
The outer edge, or outline, of the diamond's shape. This is the area where the average diameter, width and length of stones are measured. The girdle is situated in-between the pavilion (lower part) and the crown (upper part). It can be faceted, polished or unpolished in which case it looks granular.
The measurement describing the girdle thickness is the average distance between the pavilion (lower part) and crown (upper part), measured in millimeters but usually expressed in percentage of the average diameter.
"Hearts & Arrows" are usually (but not necessarily) Excellent-Ideal cuts of superior quality. Polishers used "secret recipes" to create the pattern of "Hearts" looking down through the pavilion and "Arrows" seen in the table-up position. The precision and sharpness of the patterns relied on precise angles in combination with specific facet length, width and azimuth.
A diamond polished to the highest standards in precision and perfection, resulting in ideal balance between brilliance and 'fire'. The combination of angles and proportions, as well as the highest quality of polish and symmetry ensure optimal return of light.
International Gemological Institute was established in Antwerp, Belgium in 1975, and is one of a very small number of internationally recognized laboratories issuing diamond grading reports, colored stones reports, as well as fine jewelry reports. IGI also runs gemological training courses and operates a well-known and respected research department.
A naturally occurring imperfection in a diamond, commonly referred to as "internal characteristic". Some examples are: feathers, crystals, needles, clouds and pinpoints.
Karat is the measure of purity of gold; 24-karat being pure gold. Jewelry is usually made from 18K and 14K gold, which contain other metals for strength.
A diamond enhancement technique whereby a laser is used to drill to a dark inclusion which is then bleached in order to enhance the inclusion’s appearance.
A tiny tube created during the laser drilling process of a diamond.
Is the laser-etched text put on the girdle of a diamond for identification purposes. Usually the text is the laboratory initials (IGI) and the grading report number.
A comparison of how much longer a diamond is than it is wide. It is used to analyze the outline of fancy shapes only; it is never applied to round diamonds. There's really no such thing as an 'ideal' ratio; it's simply a matter of personal preferences. For example, some people prefer the look of a long, slender marquise and others prefer the look of a shorter, fatter marquise. And while many people like square princess cuts and radiants, there are some people who enjoy more rectangular proportions for these types of fancy shapes.
A 10x magnifying lens used to examine diamonds and other gemstones.
Also called "lower halves", they are the facets on the pavilion of a round brilliant just below the girdle.
The degree to which a diamond or gemstone reflects light.
An elongated shape with pointed ends inspired by the fascinating smile of the Marquise de Pompadour and commissioned by the Sun King, Louis XIV of France, who wanted a diamond to match it.
An ancient form of the brilliant diamond with a cushion-shaped outline, high crown, small table, deep pavilion, and an extremely large faceted culet.
The 10-point scale of mineral hardness created in 1812 by the German mineralogist Friedrich Mohs. It is one of several definitions of hardness in materials science. Diamond scores 10 on the Mohs Scale, 9 for Corundum (Ruby and Sapphire), 7.5 to 8 for Beryl (emerald and aquamarine) and 7 for Quartz. Diamond is the hardest of all known natural substances.
A small rough diamond portion that can be found on some polished diamonds. This is often done so the polisher can maximize weight yield of a diamond.
The earliest known form of brilliant cut diamond with a very small table and steep crown.
A gem's intrinsic ability to interact with light. Some optical properties are color, dispersion and fluorescence.
A style of jewelry setting in which numerous small diamonds are mounted close together to create a glistening diamond crust that covers the whole piece of jewelry and obscures the metal under it.
The lower part of a polished diamond, usually cone-shaped.
The angle measured between the girdle and the pavilion main facet.
The eight facets found on the pavilion of a round brilliant diamond. They run from the girdle to the culet.
Combining the best of the oval and the marquise, it is shaped like a sparkling teardrop.
Internal characteristic: minute to very small, usually a whitish dot inside a diamond.
1/100th of a carat. For example, a 3/4 carat diamond weighs 75 points.
The way polishers finish the smoothness of facets on a diamond. Polish is graded starting at "Excellent" and followed by "Very Good", "Good", "Fair" and "Poor".
This is a square or rectangular cut with numerous sparkling facets.
The small areas of light in a polished diamond that flash on and off as the diamond, observer or lighting moves.
The shape of a gemstone. The most famous are known as round, marquise, pear, oval, heart, princess, radiant, emerald, cushion and triangle but there are also many other shapes.
One of the eight triangular facets found at the edge of the table facet and pointing to the outline of a brilliant-cut diamond.
Symmetry of individual facets, and symmetry of the parts of the stone as well as their overall alignment, is what a gemologist must observe and grade from 'Excellent' to 'Poor'.
The largest facet, situated on top of the crown of a diamond. This is where most of the light enters and exits a diamond.
The width of the table divided by the average diameter.
Also called "upper halves", they are the 16 facets found on the crown, between the girdle and the star facets.
A square or rectangular-shaped diamond with cut corners. On the crown, there are three parallel rows of facets arranged around the table and, on the pavilion, there are three parallel rows arranged around the culet. This type of cut is also known as a Step Cut because its broad, flat planes resemble stair steps. Inclusions that are visible through the table to the unaided eye.
- The RI is a constant number that indicates how much light is slowed down in a particular medium.
- The ration between the speed of light in the air and the speed of light in a particular medium.
- The ratio of the speed of light in air to its speed in a substance.
Direction of single refraction in a double-refractive stone
Determining how the light travels through the crystal. With the use of several instruments, we will be able to see if the stone is isotropic or anisotropic, uniaxial or biaxial.
Uniaxial and Biaxial gems can be positive or negative depending their crystal system. The optical sign will be given by studying the refractive indexes.
- Density is the weight per volume (g/cm³)
- Specific gravity is the density of a material at a certain temperature divided by the density of water at a certain temperature.
A written estimate of the approximate retail replacement value of the item described. They can be used for insurance purposes and should be updated every few years.
On a round brilliant diamond, these are eight large kite-shaped facets on the crown. Also called main crown facet.
Brilliance describes the reflections of white light coming from the diamond in “face-up” position. It is the effect that makes diamonds unique among all other gemstones. While other gemstones also display brilliance, none have the power to equal the extent of diamond's light-reflecting power. Brilliance is created primarily when light enters through the table, reaches the pavilion facets, and is then reflected back out through the table, where the light is most visible to your eye.
Round diamond with 57 facets (58 if there is a facet on the culet).
In this type of cutting shape, all facets appear to radiate out from the center of the diamond toward its outer edges. It is called a brilliant cut because it designed to maximize brilliance. Round diamonds, ovals, radiants, princesses, hearts, marquises, and pears all fall within this category of cut.
The standard unit of measurement of the weight of a diamond. One carat equals 1/5 of a gram or 1/142 of an ounce.
1 carat=100 points. The word Carat comes from the carob bean, whose consistent weight was used in times past to measure gemstones.
A type of inclusion consisting of a large or deep opening in the diamond.
The degree to which a diamond is free from internal characteristics and blemishes.
Clarity is graded on a scale from Flawless (FL) to Imperfect (I).
Any process used to improve the apparent clarity of a diamond. This may include filling fractures and cavities with
foreign substances such as glass or resin, depending on the stone.
A crack in a diamond which is parallel to one of its crystallographic planes. A cleavage may be caused by inherent internal strain or by a sharp blow. The crack usually extends to the surface.
A group of minute to very small, white inclusions which give a "cloudy" appearance.
A system of grading diamond colors based on their colorlessness (for white diamonds) or their spectral hue, depth of color and purity of color (for fancy color diamonds). For white diamonds, IGI uses the internationally recognized grading system which runs from D (totally colorless) to Z (light yellow).
The part of the diamond that is above the girdle. It consists of the table and the crown facets below it.
The angle measured between the girdle plane and the bezel facets. Along with the table size, the crown angle helps determine the amount of dispersion (also called "fire") displayed by the diamond.
The crown height is measured perpendicular to the girdle and is expressed as a percentage of the average girdle diameter.
A type of inclusion. A crystal is a mineral deposit trapped inside the diamond.
The point at the bottom of a full-cut diamond. Some diamonds have a faceted culet.
An antique style of cut that looks like a mix between an Old Mine Cut (see Mine Cut Diamond) and a modern oval cut.
The cut (or make) of a diamond refers both to the proportions and the finish of a polished diamond. The cut is the most important of the 4Cs (cut, color, clarity, carat) in determining the diamond’s overall beauty, and is the only man-made contribution to a diamond's beauty and value.
The distance between the table facet and the culet measured in millimeters.
Also called "total depth", this figure is expressed in % and is the result of the following calculation:
- Round-shaped diamond: the diamond’s depth divided by its average diameter.
- Fancy-shaped diamond: the diamond’s depth divided by its width.
This covers thin girdles as well as inclusions that weaken a gem.
A term used in clarity-grading: "eye-clean" diamonds should have no inclusions that are visible through the table to the unaided eye.
A polished plane on the surface of a gemstone.
Diamonds having color more intense than "Z", as well as diamonds exhibiting color other than yellow or brown are considered fancy colored diamonds. These diamonds are graded using separate systems which indicate the characteristics of the color, and not just its presence.
Any diamond shape other than round.
A fracture or break in a diamond that looks like a white feather.
The property in approximately 50% of all diamonds that makes them glow when exposed to ultraviolet light (such as the lighting frequently seen in night clubs). Diamonds can fluoresce in a number of colors, but blue fluorescence is most common. Depending on its intensity, blue fluorescence may enhance the color of some diamonds by hiding their yellow tint.
A chip or break on a diamond that is not in the direction of a cleavage plane
A treatment whereby feathers in a diamond are filled with an artificial substance. This treatment is not permanent since the filler can dissolve and escape over time.
The outer edge, or outline, of the diamond's shape. This is the area where the average diameter, width and length of stones are measured. The girdle is situated in-between the pavilion (lower part) and the crown (upper part). It can be faceted, polished or unpolished in which case it looks granular.
The measurement describing the girdle thickness is the average distance between the pavilion (lower part) and crown (upper part), measured in millimeters but usually expressed in percentage of the average diameter.
"Hearts & Arrows" are usually (but not necessarily) Excellent-Ideal cuts of superior quality. Polishers used "secret recipes" to create the pattern of "Hearts" looking down through the pavilion and "Arrows" seen in the table-up position. The precision and sharpness of the patterns relied on precise angles in combination with specific facet length, width and azimuth.
A diamond polished to the highest standards in precision and perfection, resulting in ideal balance between brilliance and 'fire'. The combination of angles and proportions, as well as the highest quality of polish and symmetry ensure optimal return of light.
International Gemological Institute was established in Antwerp, Belgium in 1975, and is one of a very small number of internationally recognized laboratories issuing diamond grading reports, colored stones reports, as well as fine jewelry reports. IGI also runs gemological training courses and operates a well-known and respected research department.
A naturally occurring imperfection in a diamond, commonly referred to as "internal characteristic". Some examples are: feathers, crystals, needles, clouds and pinpoints.
Karat is the measure of purity of gold; 24-karat being pure gold. Jewelry is usually made from 18K and 14K gold, which contain other metals for strength.
A diamond enhancement technique whereby a laser is used to drill to a dark inclusion which is then bleached in order to enhance the inclusion’s appearance.
A tiny tube created during the laser drilling process of a diamond.
Is the laser-etched text put on the girdle of a diamond for identification purposes. Usually the text is the laboratory initials (IGI) and the grading report number.
A comparison of how much longer a diamond is than it is wide. It is used to analyze the outline of fancy shapes only; it is never applied to round diamonds. There's really no such thing as an 'ideal' ratio; it's simply a matter of personal preferences. For example, some people prefer the look of a long, slender marquise and others prefer the look of a shorter, fatter marquise. And while many people like square princess cuts and radiants, there are some people who enjoy more rectangular proportions for these types of fancy shapes.
A 10x magnifying lens used to examine diamonds and other gemstones.
Also called "lower halves", they are the facets on the pavilion of a round brilliant just below the girdle.
The degree to which a diamond or gemstone reflects light.
An elongated shape with pointed ends inspired by the fascinating smile of the Marquise de Pompadour and commissioned by the Sun King, Louis XIV of France, who wanted a diamond to match it.
An ancient form of the brilliant diamond with a cushion-shaped outline, high crown, small table, deep pavilion, and an extremely large faceted culet.
The 10-point scale of mineral hardness created in 1812 by the German mineralogist Friedrich Mohs. It is one of several definitions of hardness in materials science. Diamond scores 10 on the Mohs Scale, 9 for Corundum (Ruby and Sapphire), 7.5 to 8 for Beryl (emerald and aquamarine) and 7 for Quartz. Diamond is the hardest of all known natural substances.
A small rough diamond portion that can be found on some polished diamonds. This is often done so the polisher can maximize weight yield of a diamond.
The earliest known form of brilliant cut diamond with a very small table and steep crown.
A gem's intrinsic ability to interact with light. Some optical properties are color, dispersion and fluorescence.
A style of jewelry setting in which numerous small diamonds are mounted close together to create a glistening diamond crust that covers the whole piece of jewelry and obscures the metal under it.
The lower part of a polished diamond, usually cone-shaped.
The angle measured between the girdle and the pavilion main facet.
The eight facets found on the pavilion of a round brilliant diamond. They run from the girdle to the culet.
Combining the best of the oval and the marquise, it is shaped like a sparkling teardrop.
Internal characteristic: minute to very small, usually a whitish dot inside a diamond.
1/100th of a carat. For example, a 3/4 carat diamond weighs 75 points.
The way polishers finish the smoothness of facets on a diamond. Polish is graded starting at "Excellent" and followed by "Very Good", "Good", "Fair" and "Poor".
This is a square or rectangular cut with numerous sparkling facets.
The small areas of light in a polished diamond that flash on and off as the diamond, observer or lighting moves.
The shape of a gemstone. The most famous are known as round, marquise, pear, oval, heart, princess, radiant, emerald, cushion and triangle but there are also many other shapes.
One of the eight triangular facets found at the edge of the table facet and pointing to the outline of a brilliant-cut diamond.
Symmetry of individual facets, and symmetry of the parts of the stone as well as their overall alignment, is what a gemologist must observe and grade from 'Excellent' to 'Poor'.
The largest facet, situated on top of the crown of a diamond. This is where most of the light enters and exits a diamond.
The width of the table divided by the average diameter.
Also called "upper halves", they are the 16 facets found on the crown, between the girdle and the star facets.
A square or rectangular-shaped diamond with cut corners. On the crown, there are three parallel rows of facets arranged around the table and, on the pavilion, there are three parallel rows arranged around the culet. This type of cut is also known as a Step Cut because its broad, flat planes resemble stair steps. Inclusions that are visible through the table to the unaided eye.
- The RI is a constant number that indicates how much light is slowed down in a particular medium.
- The ration between the speed of light in the air and the speed of light in a particular medium.
- The ratio of the speed of light in air to its speed in a substance.
Direction of single refraction in a double-refractive stone
Determining how the light travels through the crystal. With the use of several instruments, we will be able to see if the stone is isotropic or anisotropic, uniaxial or biaxial.
Uniaxial and Biaxial gems can be positive or negative depending their crystal system. The optical sign will be given by studying the refractive indexes.
- Density is the weight per volume (g/cm³)
- Specific gravity is the density of a material at a certain temperature divided by the density of water at a certain temperature.
