Gemstone Glossary

A metric unit measuring the weight of gemstones, including diamonds, equivalent to 200 milligrams. This standard originates from the consistent weight of carob tree seeds, which served as the ancient measure for precious gemstones.

It is grade assessing a gem's internal flaws, including inclusions and blemishes. Clarity grades, like Flawless (FL) and Very Slightly Included (VVS), provide insight into a gem's purity.

A system for evaluating the color of diamonds and moissanite. The scale spans from Colorless to Light yellow for non-fancy colored gemstones, internationally recognized with grades ranging from D (completely colorless) to Z (light yellow). Fancy-colored gemstones adhere to a separate grading system.

The upper part of a cut diamond, positioned above the girdle, comprising the table and surrounding facets. It represents the most visible portion of a diamond.

The angle formed by the surface of crown facets and the girdle plane. This angle disperses incoming light within the gemstone, influencing the 'fire' effect—a crucial factor in a diamond's brilliance.

A small cut at the pavilion's base, preventing chipping of the pointed tip. Modern culets are minimal compared to historically prominent versions, such as the Old European or Old Mine cut.

It refers to the gemstone's shaping design rather than its shape (e.g., brilliant cut). It is a vital grade in gemstone evaluation, affecting fire, scintillation, and brilliance.

The height of a gemstone, measured in millimeters from its top (table) to the bottom (culet or pavilion tip).

A gemstone's depth divided by its width, expressed as a percentage, is crucial for brilliance. Each cut, e.g., round brilliant or princess, has an ideal percentage; deviations impact internal reflection and brilliance.

The splitting of white light into its spectral colors, termed 'fire.' Determined by gemstone facet angles, it enhances the diamond's rainbow-like display. Note: Natural color is unrelated to dispersion.

It denotes responsible environmental and social practices in gemstone mining and sourcing. By eliminating mining, lab-grown gemstones are considered ethically sourced, reducing environmental impact.

A polished, flat surface on a cut diamond contributing to its brilliance. The traditional round brilliant cut gemstone comprises 58 facets, including the culet. Various gemstone cuts feature distinct facet arrangements.

Categories alternative to the round brilliant cut, e.g., princess cut, heart-shaped, fall under fancy-shaped diamonds.

The quality of a gemstone's exterior workmanship by a cutter, including symmetry, design, and polish. It doesn't relate to inherent properties but affects the gemstone's appearance. Finish grading is detailed in grading reports.

Also known as dispersion, it refers to the rainbow-like colored light seen under specific lighting conditions. Caused by white light dispersion, it adds to a gemstone's allure.

Gemstones react to ultraviolet light, emitting a soft glow (often blue or green). It is desirable for hiding a gemstone's yellowness but can sometimes give a cloudy appearance at high levels. Fluorescence varies among gems.

The laboratory process of creating gemstones, known as lab-grown gemstones.

The gemstone’s widest part, forming a narrow band, separating the crown from the pavilion. They are often etched with microscopic identification numbers. Girdles are classified by thickness.

The measure of a gem's resistance to scratching or abrasion. The Mohs scale rates hardness from 1 (softest, like talc) to 10 (hardest, like diamond).

The tiny or foreign materials trapped inside a gemstone during its formation. Inclusions can affect a gem's clarity and value.

Gemstones produced in a laboratory setting, chemically and optically identical to natural gems — a more sustainable alternative to mined gemstones.

Relevant only to fancy-shaped gemstones, this ratio compares length and width, varying by personal preference rather than strict standards.

The quality and intensity of light reflection from a gem's surface. Luster descriptions include categories like metallic, vitreous (glass-like), and pearly.

A rare mineral discovered by Dr. Moissan in 1893, renowned for its brilliance and durability. It is often used as a diamond substitute.

The region beneath the girdle, opposite the crown. In the round brilliant cut, the pavilion tapers to a pointed tip. The pavilion angle impacts internal reflection. Tips are sometimes cut to prevent chipping, called a culet.

One-hundredth of a carat, aiding precise weight measurements.

The smoothness of facet surfaces, a marker of cutter skill. It is graded from Poor to Ideal, indicating the gemstone's quality.

It measures the speed of light passing through a material. High refractive indices, as in gemstones, enhance brilliance.

The sparkle and flash seen in a gemstone's movement under various lighting conditions, resulting from light reflections and refractions.

A grading criterion separate from the 4Cs, assessing the uniformity of facet angles and symmetry. Critical for a gemstone's overall appearance, with ratings ranging from Poor to Ideal.

The largest gemstone facet, influencing the apparent size and light optimization. Typically, the most visible part of a gemstone.

Expressed as a percentage, it compares the table's width to the total diamond diameter. No fixed ideal exists; preference guides this aspect, not brilliance.