Diamond Terms: I am often asked to define diamond terms, so here is a list of the technical words most commonly requested by our visitors, all in one place.

For a more comprehensive, searchable glossary, visit the GIA Diamond Dictionary at the GIA Web site.

For brief explanations of the specific terms used on GIA Diamond Grading Reports, visit the page that explains the new report formats and services.

Go here to understand and decide about the 4 Cs.

Go here to go beyond the 4 Cs and learn how to read a certificate.

Blemish:
A flaw (scratch or abrasion) on the surface of a diamond. These are generally not considered as crucial to the beauty of a stone if they do not interfere with the symmetry of the shape and do not interfere with the flow of light through the stone.

Brilliance:
White light reflected up through the top of a diamond. Cutting a diamond to the correct proportions increases the reflection of light from the facets and maximizes the brilliance.

Brilliant Cut:
A 58-facet round diamond, sometimes still called the American Brilliant. This shape and faceting arrangement are designed for maximum brilliance, sparkle and beauty.

Carat:
A unit of weight for a diamond. Equivalent to 200 milligrams, or one-fifth of a gram. In ancient India, the carob bean was used for measuring the weight of gems, because of the rare property that every seed weighed the same. The word "carat" today is thought to be derived from the ancient "carob." Because they are increasingly rare, larger diamonds cost much more than smaller stones. Wholesale prices are listed PER CARAT to show this price difference. For instance, a 1/2-carat round brilliant diamond of G/VS2 quality would sell for $3,600 per carat ($1,800 for the stone), while a 1-carat stone of the same quality would cost $6,300 per carat ($6,300 for the stone) because it is twice the size and more rare.

Clarity:
A grade given to a diamond to describe the level of "impurities" or inclusions.

Clarity grades include:
FL = Flawless -- no internal or external inclusions of any kind visible under 10x magnification to a trained eye, the most rare and expensive of all clarity grades
IF = Internally Flawless -- no internal inclusions visible under 10x magnification to a trained eye, but there may be some tiny external irregularities in the finish
VVS-1 = Very Very Slightly Included 1 -- usually just one tiny inclusion visible only to a trained eye under 10x magnification
VVS-2 = Very Very Slightly Included 2 -- tiny inclusions visible only to a trained eye under 10x magnification
VS-1 = Very Slightly Included 1 -- very small inclusions visible with 10x magnification
VS-2 = Very Slightly Included 2 -- several very small inclusions visible with 10x magnification
SI-1 = Slightly Included 1 -- small inclusions visible with 10x magnification
SI-2 = Slightly Included 2 -- several small inclusions visible with 10x magnification
SI-3 = Slightly Included 3 -- inclusions that may be visible to the naked eye for a trained observer
I-1 = Included 1 -- flaws that are visible to the naked eye
I-2 = Included 2 -- many flaws clearly visible to the naked eye that also decrease the brilliance
I-3 = Included 3 -- many flaws clearly visible to the naked eye which decrease the brilliance and compromise the structure of the diamond, making it more easily cracked or chipped

Cloud:
A cluster of very small inclusions inside a diamond that give a cloud effect. Tiny clouds will not interfere with the flow of light, but large or numerous clouds can affect brilliance.

Color:
A grade given to a diamond to describe the subtle tones of color in a stone. D is perfectly colorless, the most rare and expensive color. As you go from D to Z on the normal color scale, it indicates increasing levels of yellow and/or brown tones. It takes a trained eye under special lighting to distinguish between neighboring color grades (such as E to F), but most people can discern the difference between colors that are several grades apart (such as E to H) with a little practice. Fancy colors such as pink, red, blue and green are discovered each year, but they are very rare and incredibly expensive. Such fancy colors do not follow the normal color/pricing scales and are categorized separately.
The normal color scale, as defined by the Gemological Institute of America:

D, E, F = Colorless
G, H, I, J = Near Colorless
K, L, M = Faint Yellow
N, O, P, Q, R = Very Light Yellow
S, T, U, V, W, X, Y, Z = Light Yellow

Culet:
A facet on the very bottom of a diamond. It is best to have a small or medium culet. A large culet will make it look like there is a hole in the bottom of the stone due to leakage of light. Absence of a culet makes the point of the diamond more easily damaged or chipped.

Cut:
Commonly used to refer to both the shape of a stone (round, pear, oval, etc.) and the make (the exact geometric proportions to which a diamond is cut). The make of a stone is the most important factor in determining how much sparkle comes from a diamond, regardless of the shape.

Ideal Cut:
Round diamonds that are perfectly proportioned (having depth percentages and table percentages that some people feel produce a "perfect" balance of fire and brilliance). They almost always have the highest grades on polish and symmetry as well, indicating the great care taken in the overall fashioning of hte stone. These diamonds have had the finest craftsmanship to maximize the beauty of the diamond.

Ideal Cut diamonds are usually more expensive than all other cut grades. This is due to three major factors: 1) extra time and skill are required to cut to such precision; 2) they are in great demand, and perhaps most importantly, 3) more of the original rough diamond must be sacrificed to achieve ideal proportions.

Very Good Cut:
Diamonds cut to fit very strict requirements for depth percentage and table percentage. These outstanding proportions maximize fire and brilliance in the diamond.

Good Cut:
Diamonds cut with acceptable, but not perfect, proportions. They generally have very good brilliance and fire and make excellent jewelry.

Fair Cut:
Diamonds cut to less perfect proportions. They have been cut to maximize the weight of the stone, and sacrifice fire and brilliance. While less expensive than diamonds shown as having Good and Very Good cuts, they do not have the brilliance and scintillation (sparkle) people expect from a diamond.

Poor Cut:
Poorly cut diamonds with proportions and finish that make them look relatively lifeless to the eye. We do not recommend such stones for fine jewelry.

Depth:
The height of a diamond (measured from the culet at the very bottom to the large table facet on the top).

Depth %:
The height of a diamond (measured from the culet to the table) divided by the width of the diamond. The depth % is critical to creating brilliance and fire in a diamond. A depth % that is too low or too high will cause light to leak out of the stone, causing the diamond to lose sparkle.

Eye-clean:
A diamond that has no inclusions visible to the naked eye -- flawless to the naked eye. This is normally true of all diamonds with a grade of about SI-1 or higher on the clarity scale.

Facet:
The polished flat surfaces on a diamond. For example, a round brilliant diamond has 58 facets when counting the culet.

Fire:
Colored light reflected from within a diamond. White light entering a stone is separated into the many colors of the rainbow just like a prism. Good fire can only be achieved with very good to excellent proportions. Also called "refraction" or most often "dispersion" in the trade.

Fluorescence:
A glow, usually of a bluish color, which emanates from certain diamonds when exposed to ultraviolet light. Strong fluorescence should be avoided, but faint fluorescence usually does not affect the appearance of a diamond. In fact, faint or moderate blue flourescence is preferred by some customers because it can make a less expensive yellowish color appear more white or colorless in daylight.

Girdle:
The narrow band around the outer circumference of a diamond. The jewelry setting usually holds the diamond around the girdle. Girdles can be rough (looks sandblasted) or faceted (polished like the rest of the diamond). Either one is good, since it makes little difference to the overall beauty of the diamond.

Inclusion:
An impurity within a diamond, such as a spot or irregularity in the crystal structure of the stone. These can include a cloud, a fracture, another diamond inside the bigger one, liquid, etc. Inclusions can either be visible with the naked eye (usually SI-3 clarity and below) or visible only under magnification. Fewer inclusions means a finer clarity grade, increased rarity, and increased value.

Make:
The quality of the finish and proportions of a finished diamond. A good make will have proportions that maximize brilliance and fire. A poor make will decrease sparkle and fire due to the loss of light as it travels through the stone.

Pavilion:
The bottom half of a diamond, from the lower girdle to the culet at the bottom tip. If the pavilion is too deep or too shallow, light will leak out and the diamond will lose fire and brilliance.

Point:
A measure of diamond weight. One point equals 1/100th of a carat. A diamond that weighs 0.50 carat is said to weigh 50 points. This does not refer to the number of facets.

Polish:
A grade given to the external finish of a stone. The polish grades from poor to excellent. Good polish is crucial for maximum brilliance of a diamond, but it takes a trained eye to distinguish between polish grades. Extra facets to remove a part of the rough are common, as well as grainy lines that are visible only under a loupe or microscope.

Sparkle:
The combination of fire (dispersion) and brilliance. The amount of light that reflects out of a diamond as it moves. This is sometimes called "scintillation" by older dealers, including ourselves.

Symmetry:
A grade given to the overall uniformity of a stone's cut, which can range from poor to excellent. Poor symmetry will hurt a diamond's sparkle and fire, due to loss of light as it flows through the stone and out to your eye. We recommend only diamonds with good to excellent symmetry.

Table:
The large flat facet on the top a diamond. If the table facet is too large or too small, it will often indicate poor proportions overall. Poor proportions will hurt a diamond's fire and brilliance.

Table %:
The width of the table divided by the total diameter of the diamond. The table % is critical to creating sparkle and fire in a diamond.

Robert Hensley
President
Diamond Helpers

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