Diamond Gemstone Properties

If you are shopping for a large diamond, .75 carat or more, you should look for a loose stone, or ask the stone be removed from the mounting if possible. When it is loose ask to see the stone weighed. Have the seller show you its color grade and show you its flaws under magnification. Look at the diamond in ordinary light, rather than under spot lights. Keep in mind that all diamonds do not look alike, to see the differences it is important to look at a few and compare them. It is especially important to look at them under normal lighting conditions, not just under the intense "diamond lights" that are prevalent in jewelry stores..

21 Minute Read

By Sondra FrancisMore from this author

There is probably no other word in the English language that creates as much excitement for so many women than diamond. Diamond is a wondrous gemstone: its hardness is unrivaled by any other substance. A properly cut diamond has outstanding brilliance and dispersion that is second to none.

At one time diamonds were reserved to adorn royalty; but today they are the most popular and available gemstone for everyone. Shopping for diamonds can be simple if a buyer is familiar with the characteristics known as the four C's. Diamonds are easier to shop than other gemstones for because diamonds have an accepted system for grading that is universal.

Colors:Most range from colorless to tints of yellow or brown. Fancy colors are rare but include blues, intense yellows, green, lavender, pink, red, oranges and browns
Durability:Tough but has perfect cleavage, protect from blows
Treatment:None common. Laser drilling and filling, irradiation and heating to produce fancy colors
Availability:Strong supply in colorless to tinted yellow in stones up to five carats
Localities:Australia, Rep. of Congo, Russia, South Africa, Botswana, Namibia
Common shapes:Rounds, marquise, pears, emerald cuts, heart shapes, modified emerald cuts such as princess cuts, quadrillions, etc.
Diamond, .85 carat, SI-1, G Color
(Photo by ICA/Bart Curren)

How to Shop for a Diamond

If you are shopping for a large diamond, .75 carat or more, you should look for a loose stone, or ask the stone be removed from the mounting if possible. When it is loose ask to see the stone weighed. Have the seller show you its color grade and show you its flaws under magnification. Look at the diamond in ordinary light, rather than under spot lights.

Keep in mind that all diamonds do not look alike, to see the differences it is important to look at a few and compare them. It is especially important to look at them under normal lighting conditions, not just under the intense "diamond lights" that are prevalent in jewelry stores.

Carat Weight and Diamond Pricing

Diamond prices are well defined according to carat weight. For stones under l.00 carat, there are ten divisions of sizes that each have their own price structure. As diamonds become larger in size the per carat price goes up steadily up to five carats. Larger diamonds have their own price structure based on their extreme rarity and demand.

For each size classification of colorless or nearly colorless diamonds, there are ten clarity grades and ten color grades used for pricing. This gives one hundred possibilities of price per carat for each particular size, not even including fancy colors, which have a completely different price structure. Every jeweler in the country has gotten a phone call asking how much a one carat diamond is going for at that moment; of course, there are a hundred different possible responses unless color and clarity are defined.


Color is the most important factor in determining the price of a diamond at a given size. Generally when we think of diamonds we think of a colorless gemstone or something that appears to be colorless.

Fancy color is applied to those diamonds that are visibly intense yellow or gold, pink, blue, green, red, orange, violet or brown.

Natural pinks, blues, greens, reds, oranges, and violets are exceptionally rare and few become available each year. Fine fancy colored diamonds have received mind-boggling prices in auction sales in recent years. At Christie's auction in April, l987 a .95 carat red diamond sold for $926,000 per carat! Yes, we said "rare and expensive!"

Natural fancy yellows and browns are more readily available. Fancy yellow fetch premium prices; fancy browns are usually available at bargain prices. Sometimes, you can also buy colored diamonds that are irradiated and heated to produce into intense yellows, bright blues, green and browns. The irradiated fancy color diamonds are priced much lower than natural fancy colors. Irradiated blue diamonds resemble the color of blue zircons; they do not resemble the natural blue color of diamonds. If you are shopping for fancy colored diamonds, ask the seller the origin of the color. When you buy a fancy colored diamond get the color and the origin of the color-whether it is natural or irradiated-written on the sales slip.

Most of the diamonds mined, sold and worn fall into the colorless to light yellow category. The Gemological Institute of America devised a an alphabetical system for diamond color grading. Letters from "D" to "Z" signify diamonds from colorless to intense yellow. "D" to "F" are grades that are truly colorless; at "G" there is a slight tinge of yellow and each subsequent letter represents an increasing amount of yellow.

Diamonds that have color grades of "G" through "K" will normally "face up" to appear nearly colorless. But from "L" to "Z" there is an obvious yellowness when the stone is viewed face up. Old terms for describing diamond colors, i.e., river, Wesselton, crystal, and others which were common during the early part of the century, do not specifically define color in any scientific manner. These terms are imprecise and confusing, but fortunately they are rarely used today in the United States.

To properly color grade a diamond, it must be loose. The diamond is placed table down, then it is compared to a set of master color grading diamonds. Master stones have been color graded by the laboratory of the Gemological Institute of America; these stones are then used to compare the color of the diamonds to be graded.

It takes an experienced knowledgeable person, generally a gemologist, to properly color grade a diamond. Lighting conditions must be controlled. If the diamond is fluorescent, this must be considered in assigning the ultimate color grade. But you still can easily see color grade differences when diamonds placed table down and compared to the master stones. Ask your seller to show you this.

Diamond prices are most heavily weighted on the color (except for diamonds that have extremely low clarity grades such as I-3). The colorless grades-D, E, and F-carry premium prices because diamonds with these color grades are extremely rare.

Color grade G, H, and I are considered fine colors, but are priced lower than the D to F grades. Colors J and K will look fine when set into a mounting but they are priced considerably lower. Price guidelines used in the trade give prices down to "M" color. "M" and below mean a diamond is are obviously yellow. At this point, the price levels out and does not change until you reach the fancy yellow colors which carry premium prices. Before a diamond is considered a fancy yellow, the color must be intense enough to be pleasing.


About 30 to 40 per cent of diamonds fluoresce. They usually fluoresce a blue color under long wave ultraviolet light, but yellow, pink, or green fluorescence also is possible. If fluorescence is slight or moderate it may have little effect on the appearance of the stone. A diamond with moderately blue fluorescence may take on a spectacular appearance when viewed in sunlight. It will appear to take on a slight blue cast and probably look better than an equal set one without fluorescence. However, if fluorescence is too strong it may cause the diamond to have an oily appearance. This is a detrimental feature.

Diamonds that fluoresce a strong yellow may assume a yellow cast but this is unusual for stones that do not have a yellow body color. Excessive fluorescence will lower the diamond's value a bit. Slight and moderate fluorescence will not affect price if the appearance in normal light is not affected.


Clarity refers to the internal inclusions and surface blemishes of a diamond. Inclusions in a diamond may be small interior crystals of diamonds or other minerals. Inclusions that appear black are called carbon spots. Internal fractures or cleavages may be referred to as feathers.

Very tiny inclusions are called pin points. A cluster of many pinpoint inclusions is called a cloud. Bearding refers to tiny cleavages that occur around the girdle of a diamond. Bearding may form during cutting or it may sometimes occur when the stone is worn. Exterior problems are called blemishes. They include chips, scratches, cavities, extra facets, and naturals, which are places where the diamond has not been polished and the original surface of the crystal remains.

The type, size, number, and placement of flaws are important factors in determining a diamond's clarity grade. If an inclusion is visible through the table it is considered more detrimental to the clarity grade than the same inclusion would be if it were closer to the girdle. Also, if the flaw is detrimental to the durability of the diamond, such as a large cleavage could be, it would have a more drastic effect on the clarity grade than if it were an included crystal. The size of flaws is very important: only the most minute flaws are found in the higher diamond clarity grades. The larger the flaw, the lower the grade. The number of inclusions also affects the clarity grade. Even when a diamond has very small flaws, if there are enough of them, the diamond could be penalized with a lower grade.

The Gemological Institute of America also devised the accepted clarity grading system. Diamonds are graded for clarity under ten power (l0X) magnification. The GIA clarity grading system includes ten clarity grades:

FLAWLESS - no visible inclusions under l0X magnification when the diamond is graded by a diamond expert; there are no detrimental surface blemishes on a flawless diamond.

VVS-1, VVS-2 - (very, very slight imperfections) The inclusions in this grade are extremely small and few in number; the inclusions would be very, very difficult to find by a diamond expert under l0X magnification.

VS-1, VS-2 - (very slight imperfection) In this grade there a few inclusions but they are relatively hard to find by a diamond expert when examined under 10X magnification.

SI-1, SI-2 - (slight imperfections) In this grade there are inclusions that are fairly easy to find under l0X magnification by an expert, but they are not eye visible without magnification. In an SI grade stone the inclusions do not obstruct the brilliance nor are they a great detriment to the durability.

I-1, I-2, I-3 - (imperfect) These grades encompass a broad range of inclusions. A better I-1 diamond may have many small flaws that do not interfere with brilliance or durability. An I-1 may have not eye visible flaws, but a lower I-1 grade can have minor problems with durability and/or have minor eye visible flaws. An I-2 grade definitely has something that is eye visible and it may have cleavages that could affect durability. Brilliance in an I-2 is definitely impaired. An I-3 grade is the lowest possibility: it will have major problems of durability and large eye visible inclusions. Brilliance is cut down considerably.

In the subgrades,"1″ is better than "2". In the VVS grade the difference between a VVS-1 and VVS-2 is extremely minor, but as the clarity grades get lower, the differences between a "1" and "2" becomes greater. There is a vast difference in the range between I-1 and I-2.

Clarity grading of a diamond is an informed opinion. It is very difficult to define in exact terms. Each diamond is individual and most will fall easily into one of the ten clarity grades but a few are debatable and fall on the border lines. Two diamond experts could disagree on the clarity grades of some stones.

When you are buying a diamond ask the seller to diagram the inclusions and point them out to you under magnification. Keep in mind you may not be able to see the smallest flaws.


The cut of a diamond determines the brilliance, dispersion and scintillation. Cut makes the diamond beautiful! Well cut diamonds will sell at a higher price per carat than diamonds which are poorly cut. The cutting of a diamond can affect the per carat price up to 25 percent, possibly more, in a given size; but it makes a one hundred percent difference in the beauty of the stone! The term cut encompasses the proportional relationships between the various parts, the quality of the symmetry and the finishing touches of polish, as well as the shape of the stone's outline.

Round Brilliant Cut Diamond

To understand the proportions of a diamond, it is easiest to start with the round brilliant cut. A round brilliant cut diamonds can be cut to maximize brilliance-the white light reflected out of the stone-and dispersion-the spectral color display. A round brilliant cut diamond has fifty-eight facets. If you place the table of a well cut diamond down on a white piece of paper with writing on it, you will not be able to read the words through the diamond! This happens because a well cut diamond is so perfectly able to trap the light that enters to that no light escapes haphazardly: it is all reflected back as brilliance. No other transparent gem material has this ability.

A poorly cut diamond will not do this either. In a diamond with poor proportions light will escape out through the pavilion and optimum brilliance is not achieved. This is especially true with fancy shaped diamonds.

What can be called a well cut diamond can be defined as a stone with defined mathematical relationships of the depth to diameter ratio, the table to diameter ratio, the crown and pavilion angles, the girdle thickness, the symmetry, and the quality of the polish. Yes, it is that complicated!

In 1919 two men, not working together but almost simultaneously, derived the mathematical proportions of an "ideal cut" diamond. In Europe, Marcel Tolkowsky and in the United States, Henry Morse came to nearly identical specifications. An "ideal cut" optimizes the brilliance and dispersion. This does not mean it maximizes both brilliance and dispersion, but combines the two factors to achieve the ultimate of beauty from the diamond. Actually it compromises the optimum aspects of brilliance and dispersion. A diamond cut just for maximum brilliance would lose dispersion and one cut to achieve maximum dispersion would lose some brilliance. Consequently the "ideal cut" is a compromise which combines both factors so the diamond has a balance of each.

Now that you know that the ideal cut maximizes the diamond's beauty you might assume that is the way all diamonds are cut and thus it is what you will buy, right? Unfortunately diamond cutting is more of a business than an art. Very few diamonds have an ideal cut because to achieve these model proportions a lot of weight would be lost when cutting from the rough crystal. The fact of the market place is that diamonds are cut to optimize yield from the rough, not beauty. Of course, if beauty is too severely compromised the diamond is less salable; consequently the cutter compromises yield a little bit with beauty.

What deviation from ideal is acceptable in a cut? Remember, when you are buying a diamond, beauty is your first consideration. A diamond will still be beautiful if the deviations from ideal fall within certain limitations.

The crown angles in well cut diamonds must be within a degree or two of Tolkowsky's 34 1/2 degrees for the crown angle and 40 3/4 degrees for the pavilion angle in order for the light to be trapped with in the diamond to produce optimum brilliance.

In an ideally cut diamond the depth percentage (which is a ratio of depth to diameter) is 60 to 6l percent. If a diamond is too shallow it will generally have a very shallow crown; with a shallow crown there is a great lessening of dispersion. If a diamond is too deep, it will appear to have a dark area in the center, hence brilliance is compromised. If all other aspects are within certain limitations, a diamond can still be quite beautiful if the depth percentage falls in between 57 and 62 percent The table of an ideal cut would range between 53 and 56 percent in ratio to the diameter but few diamonds cut today have tables below 60 percent. If the diamond has a smaller table it has sufficient crown area to display dispersion. The larger the table, the smaller the crown area and the less dispersion the diamond will display. A table between 60 and 64 percent still can have dispersion and fall into our beautiful diamond category.

The girdle on a diamond is an important portion. Ideally the girdle will comprise about one percent of the total depth. If a diamond has a very thin girdle like a knife edge it will be vulnerable to chipping on the edge; serious damage can occur due to chipping. Girdles are rated as thin, medium, slightly thick to thick to extremely thick. Medium is the most desirable. Very thick girdles can add between two and five percent to a diamond's depth; as a result, you will pay for extra weight yet you will have less brilliance. When the diamond is very deep, it will appear to be smaller in diameter than it should be. A very thick girdle often indicates excessive depth.

The symmetry of a diamond is critical to its beauty; a well cut diamond will have it facets cut with symmetrical precision. Lack of symmetry can easily be observed in older cuts of diamonds. Check to see if the pavilion is off center: under magnification view the diamond through the table, the culet will be reflected around the diamond; there appears to be about eight culets instead of one.

The crown of a diamond may not be parallel to the girdle. Girdle thickness may be uneven around the circumference of the stone. Facet shapes can be distorted. The facet relationships are very important to produce scintillation: on a well cut diamond the lower girdle facets match up exactly with the upper girdle facets. When the facets do not match, scintillation is lessened. A symmetrical table is a good indication of overall symmetry. The stone's outline should be nearly round. You can check for this by measuring the diameter of the loose diamond.

When the symmetry of a diamond is compromised in any way, the reflection of light entering the diamond is disturbed and brilliance or scintillation is lessened. Diamonds with symmetry problems are less beautiful and should sell for substantially less per carat than ones without symmetry problems. The quality of polish is essential to the luster of the diamond and is the finishing touch to the beauty. Larger diamonds of decent quality will generally have a reasonably good polish: the cutter would not sacrifice this final detail on a nice stone. However, in lower quality diamonds, cutting and polishing is often unacceptable. Small diamonds, which are referred to in the trade as melee, are sometimes not well polished. Poorly polished diamonds simply do not have optimum sparkle. Poor polish is one reason why some jewelry pieces with small diamond lack their full potential for beauty.

The girdle of a diamond generally is unpolished and may have a dull or granular appearance. On finer qualities of diamonds the girdle will often be polished or faceted. This is an extra step and a fairly expensive addition; but is a finishing touch that adds to a fine quality stone.

The modern round brilliant cut diamond evolved after the invention of the diamond saw in l9l0. Most diamond crystals are bipyramidal octahedrons.

Today these are sawed into two facetable halves. Before l9l0, the crystal was simply ground down to cut one diamond; older cuts of diamonds can easily be distinguished by excessive depth, very small tables, and large culets. Generally the facet relationships in an older cut are quite asymmetrical.

If an older cut of diamond has a squarish or cushion shape it is called an old mine cut. If it has a round shape it is an old European cut. These diamonds have a unique beauty of their own, but lack of symmetry and excessively deep proportions do not allow these diamonds to have their optimum beauty. Consequently the price per carat is generally less than a modern cut of the same weight and quality. Small diamonds or melee, which weigh under .20 carat may either be full cuts which have the full fifty-seven facets of the round brilliant cut or single cuts which have only sixteen facets; single cut diamonds are rarely larger than .05 carat. The term "chips" is usually a misnomer it almost never refers to actual chips. Almost no modern fine jewelry actually has chips in it.

Small diamonds are important accents to fine jewelry. They should be evaluated in the same way as the larger diamonds, except clarity grades are not broken down into the subgrades, the grades are just VVS, VS, SI, and I.

Fancy Shapes

Fancy shaped diamonds include the marquise, pear shape, emerald cut, heart shapes, oval, Trillion, Quadrillion, princess cut and many others. Some of these, such as the Trillion and Quadrillion, have trademarked facet arrangements. Of the fancy cuts, the marquise and the trademarked cuts are generally more expensive per carat than the round brilliant cut. The other fancy shapes will sell for less per carat that the round brilliant.

Fancy cut diamonds are not evaluated according to proscribed mathematical relationships that define the ideal round brilliant cut. Diamonds cut into marquises, pear shapes, heart shapes, and ovals lose optical efficiency just by the virtue of their shape and the maximum potential for brilliance and dispersion is less likely to be achieved.

If you are buying a fancy cut diamond you should scrutinize it very carefully. If the diamond is cut shallow, which is common for the marquises, pear shapes, and ovals, brilliance is sacrificed. When these stones are worn and get dirty, they will look very dull. A well cut but dirty round will look better. With these shapes light cannot be perfectly trapped, so besides brilliance being compromised, a bow-tie may be observable: a dark area can be seen in the center of marquises, pear shapes and ovals. The bow-tie may not be present in very shallow fancy cut diamonds; but these will obviously dull.

Emerald cuts and other cuts with square and rectangular outline shapes will often be cut very deep. Careful faceting arrangements can give rectangular outstanding brilliance. But these diamonds that are very deep will not have the surface area that the weight would suggest.

If you are buying a fancy cut diamond you must objectively look at the stone and judge its overall beauty. Observe the outline shape, is it pleasing? Long, skinny stones will lose optical efficiency. The shape may be pleasing but how is the brilliance? As a shape approaches round the more efficiently the light is reflected. Tables on fancy cuts may be quite large with the result that dispersion is compromised. So look at these very carefully and try to assess their brilliance and dispersion.

Question Private Grading Systems

Some companies may have their own diamond grading system, such as AAA or premier grade or something of that nature. As a buyer you must question what this means. Diamonds of a given size must be evaluated on color, clarity and cut; one designation cannot be used to describe all three of these. If a seller tells you, "All of our diamonds are G color with a VS-1 clarity grade," it should bring some obvious questions to mind. You, the buyer, need enough information to insure you are buying what you want.

Ready to Buy?

So what do you want when buying a diamond? A "D, Flawless with ideal cut," of course. Very fine diamonds with high color and clarity grade with an ideal cut will be visibly more beautiful than those with lesser qualifications. That is why the finer qualities command more money!

Now what can you afford? Most diamond buyers need to make a compromise in order to buy a stone that is large enough to see and still be beautiful. An ideal cut will sell for about a 25 percent premium, but you can find a well cut stone falling into the guidelines described above and still have a beautiful stone.

Color is the biggest factor effecting price. A "D" color diamond is outstanding, but even an "I" or "J" will face up nicely especially if it is set in a yellow gold mounting. Clarity grades that have no structural defects or detracting flaws will look great when the stone is worn.

The important thing is that you know the quality and you make an informed choice. It is essential that you have seen high color, high clarity grade, well cut diamonds and know how they look. Now you have a standard of beauty to compare with. The goal of the diamond buyer is to buy a truly beautiful diamond.

If your budget can afford a fine quality stone, a diamond with a VS clarity grade and "H" color or better, consider buying a diamond with a Diamond Grading Report from the Gem Trade Laboratory of the GIA. These stones have been graded by three diamond experts, they must agree on the final grade. Although the certificate has a disclaimer about this report being a "guarantee," it is pretty good insurance that you are buying the quality stated on the report. This is referred to as a certified stone in the trade. A diamond with a GIA certificate will sell for a slight premium over one with similar color, clarity, and cut, but it may be worth it for the higher qualities. There is little room for doubt concerning quality with a "certed stone." Unless the diamond has been graded by a known professional gemological laboratory, it is not truly "certed."

By Sondra Francis, G.G. – © Gem Dealers’ Secrets – Handbook for the Gem Buyer – 1999
All rights reserved internationally. Copyright © Sondra Francis, G.G.. Users have permission to download the information and share it as long as no money is made. No commercial use of this information is allowed without permission in writing from Sondra Francis, G.G.
About the Author
Sondra Francis has scoured every major colored gemstone market in the world since 1978. She was a charter member of the American Gemstone Association and served as a board member. She was a founding member of the International Colored Gemstone Association. A true gem lover, Sondra has marketed her treasures on the wholesale and retail markets.
A special thanks to Pam Dulgar, Alex Edwards, Cheryl Kremkow, Kate Kirby, Helen Mitchell, Carol Morgan Page, David Pond, Elaine Proffitt, and Ray Zajicek for their help.
Photographs: Bart Curren and ICA Gembureau ; Alex Edwards, Pearl Sales Institute ; David Dikinis

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Sondra Francis

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