Well known as a symbol of eternal and lasting love, a diamond is a gemstone apart from all other gemstones. Measuring 10 on the Mohs scale of mineral hardness, diamonds are the hardest gemstones, 58 times harder than anything in nature, and can only be scratched by another diamond.

Diamonds have been revered throughout the ages. Derived from the Greek word adamus, meaning “invincible”, diamonds are aptly named. Legend has it that the Greek god Chronos had changed a young man called Adamas into a precious stone which gave him unbelievable strength and good fortune. The Greek philosopher Plato wrote about diamonds as living beings that embodied celestial spirits.

Ancient Romans thought that diamonds were the tears of the gods or splinters that had broken off of falling stars and that Cupid’s arrows were tipped with diamonds while the Hindus believed diamonds were created when bolts of lightning struck rocks.

Various cultures have attributed exceptional healing properties to diamonds, believing they have the ability to cure stomachaches, memory loss, depression, fatigue, infections, mental illnesses, nightmares, skin diseases, and other head and heart ailments.

Diamonds are commonly known to be the hardest substance found on earth. What is less well known is that, despite being 58 times harder than any other material in nature, diamonds can be broken and are not as tough as jadeite jade. Though seemingly contradictory these facts make sense once the definitions of hardness and toughness in the gemological world are understood.

The most universally accepted grading system for diamonds is one developed by GIA (Gemological Institute of America), the Four C’s, which are color, clarity, cut and carat weight.

Although generally considered colorless, most diamonds are slightly yellow or brown. When evaluating color in a diamond, with the exception of fancy colored diamonds, it’s the absence of color that determines the grade. The less color a diamond has, the finer the grade, and the more valuable the stone.

GIA’s Color Scale begins at D (colorless) and runs to Z (light yellow). Each letter grade represents a range of color, though, rather than one specific color.

In weights less than 0.25 carat, E- and F- color diamonds appear virtually colorless; only experienced graders can distinguish them consistently, and then only in unmounted stones.

G, H, and many I diamonds appear colorless face-up when mounted. Most trained graders and experienced professionals can see color in these stones if they are not mounted, but most consumers see none at all unless they are loose and next to a D- or E- color stone.

Face-up and mounted in yellow gold, J, K, and L diamonds weighing less than 0.50 carat look very nearly colorless, but customers can usually see some color in larger stones, and in those mounted in white metal. Beyond M, most customers can see color pretty easily in any diamond larger than 0.25 carat, and as the grade gets close to Z, they can see it regardless of size. Although light yellows and browns are graded on the same scale, most people see the yellows more easily than browns of the same grade.

Clarity refers to the presence of internal features such as breaks or foreign bodies, called inclusions (or flaws), within a diamond, and to external imperfections such as scratches or blemishes. Both blemishes and especially inclusions lower the clarity grade and the value of a diamond but, in most cases, they have very little effect on a stone’s beauty or durability.

First of all, let’s go over the different areas of a cut diamond as illustrated above. The largest facet is the top surface of the diamond called the table. Surrounding the table are the facets that make up the crown of the stone. Extending from the table, the crown continues down to the girdle, the outermost edge of the stone that defines its perimeter. The girdle can vary in thickness from stone to stone. A girdle that is too thin will be at greater risk of being damaged while a girdle that is too thick will throw off the weight ratio resulting in a stone that is smaller in diameter than its weight would suggest. The pavilion is the bottom portion of the diamond extending from the girdle to the culet, the facet at the bottom of the gemstone. A well cut pavilion is very important as it will allow the optimal amount of light to pass through the stone and out of the crown, increasing its brilliance. A pavilion depth that is too shallow or too deep will allow light to escape from the side of the stone, or leak out of the bottom. The culet, the point at the bottom of the cut stone, is the most easily damaged part of the stone so extreme care must be taken when handling loose gemstones of any type. Once set the culet is more protected by the setting and less likely to be damaged, unlike the girdle, which is still exposed when set in a prong setting.

The GIA Cut Grading System for the standard round brilliant diamond evaluates seven components. The first three consider the diamond’s overall face-up appearance and are:

Brightness:   Internal and external white light reflected from a diamond.

Fire:  The scattering of white light into all the colors of the rainbow.

Scintillation:   The sparkle a diamond produces, and the pattern of light and dark areas caused by reflections within the diamond.

The remaining four, weight ratio, durability, polish, and symmetry, assess a diamond’s design and craftsmanship. The design and craftsmanship of the diamond considers weight ratio (weight of the diamond relative to its diameter), the diamond’s girdle thickness (which affects its durability), the symmetry of its facet arrangement, and the quality of polish on those facets.

Most people know that the size of diamonds and other gemstones are measured in carats. What is not always understood is that a carat is actually a unit of weight with one carat equaling 0.200 grams and almost 142 carats making up on ounce. Unlike the avoirdupois system of weights based on pounds and ounces, carats are metric and broken down by points with 100 points equaling 1 carat. Therefore a 1 point diamond equals .01 or 1/100 carats, a 10 point diamond equals .10 or 1/10 carats, a 25 point diamond equals .25 or 1/4 carats, ect.

With loose gems weight is easily determined with a scale, with mounted diamonds weight can be calculated with careful measurements. A round one carat diamond that is well cut will be approximately 6.5mm in diameter. As mentioned previously, however, a poorly cut diamond of the same weight can actually appear smaller with a diameter measuring less than 6.5mm. When the girdle, or the crown or pavilion for that matter, is too thick the height of the diamond is increased and the circumference (the length around a circle) is decreased. Since diamonds, when set, are best viewed from the top down and the height is not seen from this angle, the diamond appears smaller.

All else being equal, diamond price increases with carat weight, because larger diamonds are rarer and more desirable. But two diamonds of equal carat weight can have very different values (and prices) depending on three other factors within the 4Cs: clarity, color, and cut.