The weight or size of a diamond is measured in carats (ct.).
One carat weighs 1/5 of a gram and is divided into 100 points, so a diamond weighing 1.07 ct. is referred to as “one carat and seven points.”
- 0.75 carat = 75 points
- 1/2 carat = 50 points
- 1/4 carat = 25 points
With an accuracy of 1/100,000 carat, the IGI scales provide a highly precise diamond weight, down to the hundredth or thousandth of a carat.
It is important to note that diamonds of the same weight don’t necessarily have the same size appearance. Those cut too shallow or deep may look small for their weight, or suffer in brilliance. As a reference, IGI recommends the following vertical spreads for round brilliant diamonds.
When diamonds are mined, large gems are discovered much less frequently than small ones, which make large diamonds much more valuable.
Diamond prices rise exponentially with carat weight. So, a 2-carat diamond of a given quality is always worth more than two 1-carat diamonds of the same quality.
Most diamonds of gem quality used in jewelry vary in shade from completely colorless down to a visible yellow or brown tint.
The rarest and most expensive are diamonds in the colorless range graded D,E and F on a scale that descends to Z. Diamonds with more color than Z, or in other shades such as orange, pink, blue, etc. are classified as “Fancy Colored Diamonds” and are graded on the IGI Colored Diamond Report.
To determine the correct color, all submitted diamonds are compared to an internationally accepted master set of stones, the colors of which range from D, or colorless (the most sought after) to Z, the most yellow/brown – aside from “fancy” yellow or brown.
IGI assigns a color grade for diamonds in the D-Z range with the diamond face-down and viewed through the pavilion. This is because size, shape, cut quality and the presence of fluorescence can influence visible face-up color. In fact, lighting, mounting choice and even the clothes one wears have an impact on color, so IGI uses the most neutral environment possible to ensure accurate and consistent results.
Since diamonds form under extreme heat and pressure, internal and external characteristics are common. These characteristics help gemologists separate natural diamonds from synthetics and simulants, and identify individual stones.
There are two types of clarity characteristics: inclusions and blemishes. In order to grade the clarity of a diamond, it is necessary to observe the number and nature of external and internal characteristics of the stone, as well as their size and position. The difference is based on their locations: inclusions are enclosed within a diamond, while blemishes are external characteristics. IGI grading reports show plotted diagrams of clarity characteristics marked in red for internal and green for external features.
While nature determined the color and clarity of a natural diamond, man is responsible for the cut quality which brings it to life. The planning, proportions, cutting precision and details of finish determine how brilliant, dispersive and scintillating the diamond will be. If the cutting factors under man’s control are not optimized, the appearance of the diamond can be adversely affected.
Diamond faceting has changed over time, particularly as lighting has evolved. There are many shapes and cutting styles, each with different visual properties. The most popular diamond in the age of modern electric lighting is the Round Brilliant.
When a ray of light touches the surface, part of it is reflected back. This is called external refraction. The rest of the ray penetrates the stone and moves through it. This is known as refraction. The part of the ray reflected back to the surface exits, broken into spectral colors in a prism-like effect. This is known as dispersion. All of these elements contribute to the appearance of a diamond.
Elements of diamond beauty can be described as brilliance (all light returning to the eye), dispersion or ‘fire’ (seen as white light is broken into spectral colors), contrast patterns (contrasting light and dark areas created by the viewer’s reflection) and scintillation or ‘sparkle’ (seen as the diamond, the light source or the observer move). These qualities combine to create the life of the diamond and the way it reacts to lighting and environment.
Click on a term to read what it means.
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.
Brilliant Cut Diamond
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.
Crown Height Percentage
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 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.
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 and Arrows (Pattern)
“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.
Laser Drill Hole
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.
Mine Cut Diamond
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.
Old European Cut
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.
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.
See Emerald Cut.
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.