Diamond and Simulant Comparison Chart

Compliments of
The International Gem Society - WE ARE A MEMBER OF THIS SOCIETY

DIAMOND
April's Birthstone

Diamond Information

CHEMISTRY C
CRYSTALLOGRAPHY Isometric
REFRACTIVE INDEX 2.417
HARDNESS 10
SPECIFIC GRAVITY 3.515
CLEAVAGE Perfect 4 directions
HEAT SENSITIVE No

WEARABILITY* Excellent
SPECIAL CARE INSTRUCTIONS None

ENHANCEMENTS Some colors produced by irridation, common. Laser drilled to remove inclusions, common. Cracks filled with glass, occassional.

*Wearability is graded as Excellent, Very Good, Good, Poor, and Forget It!
For more details see the article on "Hardness and Wearability."

... Diamonds are our most popular gem. They have great brilliance, plus the delightful quality know as fire, or dispersion. (That is the ability to take in white light and throw back flashes of color.)
...Diamonds are graded into dozens of categories. While this is helpful to the professional, it can be confusing to the average consumer. I especially feel for the young couple looking for their first diamond engagement set. They want to gather enough information to make an intelligent decision, but can be overwhelmed by all the data thrown at them.
...To help you I have done two things. First, there is a description of how diamonds are graded. Once you understand that, I make recommendations on chosing a diamond. Please read on.

DIAMOND GRADING

COLOR
CLARITY
CUT
CARAT

COLOR

...The closer a diamond is to being colorless, the greater it’s value. When the current grading system was introduced in the 1930’s, diamonds were commonly called grade A, B, or C. So the current system began color grading with the letter D, to avoid any confusion.
... Colors D, E and F are the highest grades. They are described as “near colorless.”
... Colors G, H, I and J come next. They are described as “white.”
... The colors from K to Z are tinted, (usually yellow or yellowish brown.) Those that are just lightly tinted, K, L and M are often said to “set white.” That means that they are so lightly tinted that they will appear white if set in yellow gold. You would however notice their color if set in white gold or platinum.
... As one gets further down the alphabet, the tinting gets stronger and the value lower. That is, until you get to the extreme. As the color becomes richer, you have a fancy colored diamond, rather than an off colored one. Then the value starts going up again.
... Color grading is done by placing a diamond next to a set of previously graded gems. The color is compared to the graded gems to see which it comes closest to matching.
... While this low tech approach is accurate, it is also expensive and time consuming. A compromise is often made on smaller gems, by grading batches within a range, rather than coming up with a specific grade. You will usually find diamonds under a carat graded as GH, or IJ, meaning that they are in that range.
... This information is meaningful and saves you quite a bit of money. It costs over $100 to accurately grade a diamond. If you have a large diamond, where subtle differences in quality grades make a significant difference in price, then it is worth while. However, that isn’t cost effective for the majority of gems.

CLARITY

...The clarity of a diamond is determined by the size and number of inclusions inside of it. An inclusion can be another mineral, a fracture or occasionally a void. Simply put, it is anything that will interfere with the free passage of light.
... Just like with color, there are many clarity grades. They are judged by what an expert can see at 10 power magnification, under ideal conditions. The highest grade a diamond can get is Flawless. That means no inclusions can be seen at 10 power magnification. It does not mean inclusions can’t be found with higher magnification, nor should you assume it is the only grade with no inclusions visible to the naked eye.
... Clarity grades use the letters V, S and I. They stand for Very, Small, and Inclusion. Progressing from Flawless, the grades are VVSI1, (Very, Very Small Inclusions One,) VVSI2, VSI1, VSI2, SI1 then SI2. These are the grades of diamonds that have no “eye visible” inclusions, those that can’t be seen with the naked eye. (Note, some SI2 stones will have small, eye visible inclusions.)
... As we progress down the grading scale, there is I1 and I2. These have eye visible inclusions, but are still considered to be gem grade.
... Then there is P1 and P2. They are not usually considered gem grade because so little light will pass through them. However, since they have the magic name diamond, they do show up on the market regularly.
... Beware of ads “1 carat diamond ring, $299.” Just because something is a diamond, doesn’t mean it is a gem. In fact, the vast majority of diamonds mined are usually considered “industrial grade” and are used as abrasives. Many of these "industrial grade diamonds," those graded as P1 and P2, find their way into jewelry simply because they had the advertising appeal of being diamonds.

CUT

...This one of the hardest properties to judge, plus there are a number of factors to consider. The first one has to do with the brilliance of the gem.
... The pavilion facets of the gem are intended to act as mirrors, to reflect the light entering the stone, back towards the observer. However, the angle they are cut at has a lot to do with how efficiently they work. Note: If you are unfamiliar with this terminology, see our article on “Gem Cutting Terms.")
... The ideal angle for diamond pavilion facets is 41 degrees. This is usually quite convenient, based on the shape of a standard diamond crystal. Unfortunately, not all mined diamonds are in excellent proportions. The diamond cutter is often faced with having to compromise between maximum brilliance and maximum yield. The economics are such that, if the cutter removes too much material from the original crystal, there is no profit in it. Hence, many diamonds get cut at less than ideal proportions.
... Diamonds have a high refractive index, which gives them their great brilliance. A little cheating here or there is insignificant. However, if the cutter varies a little further from the ideal the brilliance begins to suffer. Still more and you get a gem that just doesn’t stand up to others in terms of brilliance or fire.
... There are no standards for this. Most jewelers are familiar with correct proportions and can judge it from the shape. The best test for most of us is to simply compare the gems side by side. If you have two diamonds of the same grade and one is significantly brighter than the other, the cut is the difference.
... Please understand that the above discussion assumes we are talking about round diamonds. Because of their symmetrical proportions, all the major facets can be cut at the same angle. The same does not hold true for other shapes.

... Many people prefer a marquis shape. This is fine, but do not expect a marquis, or any other shape, to be as brilliant as a round. On a marquis it is necessary to cut a number of facets to accommodate the shape. The angles these facets get cut at vary, slightly to greatly, from those that give the greatest brilliance. This is a simple fact of physics: the more facets that are cut at the ideal angle, the greater the brilliance of the gem.

... When looking for diamonds you may come across the terms, "Single Cut,” “Old Mine Cut” or “European Cut.” These are gems that only have eight facets running from the girdle down and eight up to the table. That makes a total of 17 facets. A standard round brilliant cut has 57 facets.
...These “single cuts” are usually used on small accent stones, but occasionally you will find an older diamond of decent size with this cutting. Obviously, these gems won’t have the brilliance of a full cut diamond, therefore they aren’t worth as much.
... Another factor that comes under the heading of cut have to do with the shape of the gem. An ideal cut gem should be symmetrical, not lop sided. This point should be obvious, but sometimes it is helpful to point it out. A misproportioned gem can be camouflaged in it’s setting and you might not notice it until you have paid for it. This may not bother you, but it might lead to dissapointment.
... Though hard, diamonds are also somewhat brittle. (If this doesn’t make sense to you, see the article on Hardness and Wearability.) The girdle of the gem is the widest part when viewed from the top and the thinnest when viewed from the side. If cut too thin, it can present a weak area that is just asking for trouble. These illustrations will give you an idea of what normal proportions are. Some girdles get cut to a knife edge and this is definitely something to be avoided.

CARAT

...This is by far the easiest of the factors to understand. Simply put, smaller diamonds are more common than large ones. Therefore smaller diamonds cost less per carat than large ones.
... If you were to see a diamond broker's price list, under each grade, the price per carat would go up with size. A grade of diamond that would cost $900 per carat in the ½ carat size might cost $1100 per carat at ¾ of a carat and $4000 in a full carat.

CHOOSING A DIAMOND

... You should spend six months income on an engagement ring. I know that, I heard it on television! For a salesman that is a great idea. However, picking a diamond is something much more personal than finances.
... Economics vary from person to person and family to family. I wouldn’t presume to advise you on how much you can afford, but I can help you wade through the morass of grading information and put it in common language.
... As a rule, I suggest diamonds that are in the white range of color, (G, H, I or J,) and those with clarity grades SI1 or SI2. Visually these are wonderful diamonds. They are bright and lively they will dazzle all your friends!
... You might consider a lower grade of color if the right deal was presented to you. An L graded diamond can look white in a yellow gold setting and be quite brilliant. The fact that it costs less per size might be worth your while. I wouldn’t recommend looking for this grade, but if you found one in a setting that you really love it would be worth serious consideration.
... Going down in clarity grading can occasionally be worth your while too, depending on the individual diamond and setting. Sometimes the “eye visible” inclusion that got it that ranking is insignificant and the overall appearance is still delightful.
... Going down further in quality is rarely worth while. I know a lot of jewelers make their living by supposedly underselling the competition, when in fact they are selling lower grade gems. Without better quality diamonds near by to compare with, the customer is often convinced they are getting a great deal. The diamonds sparkle, the price and terms are just, oh, so sweet!
... The disappointment comes later. Imagine your fiancé showing off her engagement ring, (something they usually get great joy out of,) only to find hers is dull compared to those of her friends. You no longer have a great deal. The enjoyment of the diamond goes way down when you compare a lower quality gem to a good one.
... Please consider this factor carefully! While choosing a diamond is a personal thing and not everyone will have the same opinion, most folks will get more enjoyment from a higher quality dazzler, than a larger but mediocre gem.
... How about going up in quality? That is a personal matter. If you get an emotional boost from owning the biggest and the best and can afford it, then you certainly should. However, for most people who simply want a fine gem on their finger, it isn't necessary.
... People who are serious about their diamonds and get to look at a lot of them, get a real joy out of finding those rare gems that are nearly colorless or nearly clean under magnification. These gems are much rarer and therefore demand a higher price. But that does not mean they are much prettier, nor does it mean that you will get more enjoyment out of them.
... If you were to set two well cut diamonds side by side, one graded D, VVSI1 and the other G, SI1, you would see very little, if any, difference with the naked eye. You would have a strong emotional reaction when you heard the prices though!
... The point is simple, these are the rarest quality gems and the difference is only apparent to the sophisticated diamond appraiser who inspects them carefully with magnification.


... There is occasionally a difference between a diamond graded SI1 and SI2. (SI1 is defined as “small inclusions, somewhat easy to find.” SI2 is defined as “small inclusions easy to find.”) When I look at a gem graded SI1 I usually see something like the first illustration. One or two tiny dark spots that have no effect on the brilliance of the gem.
... Those graded SI2 have inclusions placed near the center where they are more visible, or many more of them. Some gems graded SI2, like the first illustration, will have no significant difference in brilliance. In an extreme case, where there are many inclusions, (even though none are large enough to be seen without magnification,) they may make up 5% or more of the visible area. That means a 5% or more reduction in brilliance.
... One of the most important elements of a diamond's appearance is the cut. This is a difficult element to judge. Diamonds are rarely cut to ideal proportions, but they have such high optical properties that most of them are still beautiful. Without getting overly technical, you can judge the quality of cutting by simply comparing diamonds side by side. Look for overall brilliance and fire; those little flashes of color. If the diamond you are considering does not have the sparkle of the other gems, then keep looking.
... To summarize, it is usually best to go with quality rather than size, but if your budget is limited the rarest qualities may not be worth your money.

DIAMOND LOOK ALIKE COMPARISON CHART

Compliments of
The International Gem Society

... One of the biggest challenges for a new gemologist is separating diamonds from their look alikes. The keys to identifying these gems are specific gravity and birefringence.
... The following stones are arranged by specific gravity. Note that there are only three pairs of stones that share the same specific gravity, (the ones in red.) In each case, one is doubly refractive and the other is not. This makes the separations simple.

...It appears that zircon, which is occasionally isometric, could be confused with YAG. However, anytime zircon becomes singly refractive, the specific gravity drops below that of YAG.

* Moisanite has the unique property of being theromoluminescent. By gradually heating it, it will change color. Around 150 degrees Fahrenheit it starts turning light brown and as the heat increases it becomes bright yellow or green. Of course, you need to do this very gradually, as a rapid temperature change could damage some of the other stones.

International Gem Society

Dedicated to bringing quality information and educational services to everyone interested in gemstones.

GIA's New Diamond Cut Grading System

by Don Clark CSM IMG
President
International Gem Society

New Cut Grades Excellent, Very Good, Good, Fair, Poor

Excellent Grade Excellent Grade has high brilliance, scintillation and an even pattern of light and dark areas. Very Good Grade This grade also has high brilliance and scintillation, but expect them to be a bit darker in the center or around the edges. In some cases a diamond can have top brilliance and scintillation, but be down graded by its pattern. The stone above has a splintery pattern that prevents it from being graded excellent. Good Grade This grade will be generally be a bit darker or lacking in scintillation. The stone above is dark around its girdle. A stone can also be downgraded by its pattern, or its weight ratio. I.E. if it weighs more than an average gem of this diameter, it will be downgraded one step. Fair Grade A gem in this category will have very little brilliance or scintillation. The stone in the picture has a very dark ring around the girdle and a dark table area. Poor Grade Diamonds in this category have very poor proportions and show very little brilliance or scintillation. Expect to see "nail heads", where the diamond is black in the center and "fish eyes" where the brilliance washes out in the middle. Many poor grades will have a decent appearance, but be downgraded by their weight ratio.

The Components

Visual Criteria
...1. Scintillation The small areas of light in a polished diamond that flash on and off as the diamond, observer or lighting moves. There are also negative scintillation effects which include windowing, dark centers and dark upper girdles.
...2. Pattern The arrangement of light and dark areas that result from internal and external reflections.
...3. Contrast The relief of light and dark areas that creates the face-up pattern of a diamond.

Physical Components
...1. Weight Ratio A comparison of a diamond's weight in relation to its diameter.
...2. Durability This covers thin girdles as well as inclusions that weaken a gem.
...3. Polish The criteria remains the same, considering the overall quality of the polish, scratches, nicks, chips, etc.
...4. Symmetry Refers to the outline of the stone, facet arrangement and pointing, table and culet centering.

Changes

New GIA Diamond Grading Reports

Updating GIA Diamond Grading Reports

Though inclusions can affect brilliance, they are not considered in the cut grade.

The new cut grades only apply to round brilliant cut diamonds in the D to Z color range. Champagne colored diamonds cannot be fairly compared with near colorless stones.