Term

Definition

Source & Link

4 C's

The four characteristics used to evaluate diamond quality: Carat, Colour, Clarity, and Cut. This grading system was established to create standardized diamond evaluation.

GIA - 4Cs of Diamond Quality<br>https://www.gia.edu/diamond-quality-factor

Carat (ct)

The unit of weight measurement for diamonds and gemstones. One carat equals 0.2 grams or 200 milligrams.

GIA - Diamond Carat Weight<br>https://www.gia.edu/diamond-carat-weight

Carob Seeds

Seeds from the carob tree (Ceratonia siliqua) that ancient gem traders used as counterweights for measuring gemstones, believing they had uniform weight. The word "carat" derives from this practice.

GIA - Carat Weight History<br>https://www.gia.edu/diamond-carat-weight

Colour Grade (Diamond)

A measure of how colourless a diamond is, graded on a scale from D (colourless) to Z (light yellow or brown). The evaluation is conducted under controlled lighting conditions comparing the diamond to master stones.

GIA - Diamond Colour<br>https://www.gia.edu/diamond-colour

D Colour

The highest colour grade for diamonds, indicating a completely colourless stone with no detectable colour when viewed face-down through the pavilion.

GIA - Diamond Colour Scale<br>https://www.gia.edu/diamond-colour

E Colour

The second-highest colour grade for diamonds, indicating a colourless stone with minute traces of colour that are difficult to detect even by trained graders.

GIA - Diamond Colour Scale<br>https://www.gia.edu/diamond-colour

F Colour

Colour grade indicating a colourless diamond with slight colour detectable only by expert gemologists under controlled conditions.

GIA - Diamond Colour Scale<br>https://www.gia.edu/diamond-colour

G-H Colour

Colour grades in the "near colourless" range where slight colour may be noticeable when compared to higher colour grades but appears colourless when viewed alone.

GIA - Diamond Colour Scale<br>https://www.gia.edu/diamond-colour

Fancy Colour Diamond

Diamonds that exhibit intense, vivid colour outside the normal D-Z range (such as blue, pink, yellow, green). These are graded on a different scale based on colour intensity.

GIA - Coloured Diamonds<br>https://www.gia.edu/coloured-diamonds

Clarity

The evaluation of internal and external imperfections (inclusions and blemishes) in a diamond, graded under 10x magnification.

GIA - Diamond Clarity<br>https://www.gia.edu/diamond-clarity

Inclusions

Internal characteristics or imperfections within a diamond, including crystals, feathers, clouds, and other naturally occurring features formed during crystallization.

GIA - Diamond Clarity<br>https://www.gia.edu/diamond-clarity

Blemishes

External imperfections on the surface of a diamond, such as scratches, nicks, or polish marks.

GIA - Diamond Clarity<br>https://www.gia.edu/diamond-clarity

FL (Flawless)

Highest clarity grade indicating no inclusions or blemishes visible under 10x magnification by a skilled grader.

GIA - Clarity Scale<br>https://www.gia.edu/diamond-clarity

IF (Internally Flawless)

Clarity grade indicating no inclusions visible under 10x magnification, with only insignificant surface blemishes.

GIA - Clarity Scale<br>https://www.gia.edu/diamond-clarity

VVS1, VVS2 (Very Very Slightly Included)

Clarity grades indicating minute inclusions that are extremely difficult for a skilled grader to see under 10x magnification. VVS1 inclusions are slightly more difficult to see than VVS2.

GIA - Clarity Scale<br>https://www.gia.edu/diamond-clarity

VS1, VS2 (Very Slightly Included)

Clarity grades indicating minor inclusions that are difficult to see under 10x magnification. VS1 inclusions are slightly more difficult to see than VS2.

GIA - Clarity Scale<br>https://www.gia.edu/diamond-clarity

SI1, SI2 (Slightly Included)

Clarity grades indicating noticeable inclusions under 10x magnification that may be visible to the naked eye, particularly in SI2 grades.

GIA - Clarity Scale<br>https://www.gia.edu/diamond-clarity

I1, I2, I3 (Included)

Clarity grades indicating obvious inclusions visible under 10x magnification and to the naked eye, which may affect the diamond's transparency, brilliance, and durability.

GIA - Clarity Scale<br>https://www.gia.edu/diamond-clarity

Eye-Clean

Industry term describing a diamond whose inclusions are not visible to the unaided eye when viewed from a normal viewing distance (approximately 6-12 inches).

Industry terminology (not official GIA term)<br>https://www.gia.edu/diamond-clarity

10x Magnification

The standardized magnification level (10 times actual size) used by gemologists to grade diamond clarity using a jeweler's loupe.

GIA - Diamond Grading<br>https://www.gia.edu/diamond-clarity

Loupe

A small magnification device used by jewelers and gemologists, typically providing 10x magnification for diamond examination and grading.

GIA - Gemological Tools<br>https://www.gia.edu/gem-identification

Cut

How well a diamond's facets interact with light, determined by the proportions, symmetry, and polish of the diamond. Cut is the only C determined by human craftsmanship rather than nature.

GIA - Diamond Cut<br>https://www.gia.edu/diamond-cut

Cut Grade

GIA's assessment of a diamond's light performance and visual appearance, graded as Excellent, Very Good, Good, Fair, or Poor. Note: GIA only provides cut grades for round brilliant diamonds.

GIA - Diamond Cut Grading<br>https://www.gia.edu/diamond-cut

Excellent Cut

Highest cut grade indicating superior light performance with exceptional brilliance, fire, and scintillation.

GIA - Cut Scale<br>https://www.gia.edu/diamond-cut

Very Good Cut

Second-highest cut grade indicating very good light performance with slightly less optimal proportions than Excellent.

GIA - Cut Scale<br>https://www.gia.edu/diamond-cut

Light Performance

How effectively a diamond interacts with light, encompassing brightness, fire, and scintillation. Well-cut diamonds return maximum light to the viewer's eye.

GIA - Diamond Light Performance<br>https://www.gia.edu/diamond-cut

Light Return

The amount of light that enters a diamond and returns to the observer's eye, determining the diamond's brightness and brilliance.

GIA - Cut Quality<br>https://www.gia.edu/diamond-cut

Crown

The top portion of a diamond above the girdle, consisting of the table, star facets, bezel facets, and upper girdle facets.

GIA - Diamond Anatomy<br>https://www.gia.edu/diamond-anatomy

Pavilion

The bottom portion of a diamond below the girdle, designed to reflect light back through the crown to create brilliance.

GIA - Diamond Anatomy<br>https://www.gia.edu/diamond-anatomy

Girdle

The widest perimeter of a diamond, forming the separation plane between the crown and pavilion.

GIA - Diamond Anatomy<br>https://www.gia.edu/diamond-anatomy

Table

The largest facet on the top (crown) of a diamond, typically octagonal in round brilliants.

GIA - Diamond Anatomy<br>https://www.gia.edu/diamond-anatomy

Facet

A flat, polished surface on a diamond. The number, arrangement, and precision of facets determine how light interacts with the diamond.

GIA - Diamond Facets<br>https://www.gia.edu/diamond-anatomy

Proportions

The relationship between the diamond's dimensions and angles, including depth percentage, table percentage, crown angle, and pavilion angle. Proper proportions are critical for optimal light return.

GIA - Diamond Proportions<br>https://www.gia.edu/diamond-cut

Depth Percentage

The height of a diamond (from table to culet) divided by its average diameter, expressed as a percentage. Affects light performance and how large the diamond appears.

GIA - Diamond Proportions<br>https://www.gia.edu/diamond-cut

Table Percentage

The width of the table facet expressed as a percentage of the diamond's average diameter. Affects the balance between brilliance and fire.

GIA - Diamond Proportions<br>https://www.gia.edu/diamond-cut

Symmetry

The exactness of shape and placement of facets in a diamond. Poor symmetry can negatively impact light performance.

GIA - Diamond Symmetry<br>https://www.gia.edu/diamond-cut

Polish

The quality and smoothness of a diamond's surface finish. Poor polish can diminish brilliance and light return.

GIA - Diamond Polish<br>https://www.gia.edu/diamond-cut

Round Brilliant

The most popular diamond shape with 58 facets (including the culet), mathematically optimized for maximum light return. The only shape for which GIA provides a cut grade.

GIA - Diamond Shapes<br>https://www.gia.edu/diamond-shape

Fancy Shape

Any diamond shape other than round brilliant, including oval, princess, emerald, cushion, radiant, pear, marquise, and heart.

GIA - Diamond Shapes<br>https://www.gia.edu/diamond-shape

Oval Cut

An elongated brilliant-cut diamond with an elliptical outline, typically containing 56-58 facets. Ovals have more surface area than rounds of the same carat weight.

GIA - Diamond Shapes<br>https://www.gia.edu/diamond-shape

Emerald Cut

A rectangular step-cut diamond with cut corners, featuring parallel facets that create a "hall of mirrors" effect. Requires high clarity due to its transparent faceting.

GIA - Diamond Shapes<br>https://www.gia.edu/diamond-shape

Cushion Cut

A square or rectangular brilliant-cut diamond with rounded corners and larger facets, resembling a pillow. Available in various faceting patterns. Also available as an elongated cushion.

GIA - Diamond Shapes<br>https://www.gia.edu/diamond-shape

Radiant Cut

A rectangular or square brilliant-cut diamond with trimmed corners, combining the step-cut appearance of emerald cuts with the brilliance of round diamonds.

GIA - Diamond Shapes<br>https://www.gia.edu/diamond-shape

Step Cut

A cutting style featuring rows of facets that are parallel to the girdle, arranged like staircase steps. Used in emerald and Asscher cuts.

GIA - Cutting Styles<br>https://www.gia.edu/diamond-shape

Brilliant Cut

A cutting style designed to maximize light return through triangular and kite-shaped facets that radiate from the center. Used in rounds, ovals, and many other shapes.

GIA - Cutting Styles<br>https://www.gia.edu/diamond-shape

Bowtie Effect

A dark bow-tie shaped shadow that appears across the center of some elongated fancy shapes (ovals, pears, marquises) due to light leakage. Well-cut stones minimize this effect.

GIA - Fancy Shape Considerations<br>https://www.gia.edu/diamond-shape

Face-Up Appearance

How a diamond looks when viewed from directly above (the normal viewing position when worn), as opposed to viewing from the side or pavilion.

GIA - Diamond Viewing<br>https://www.gia.edu/diamond-cut

Surface Area

The visible area of the diamond's crown when viewed face-up. Shapes like ovals and marquises have more surface area than rounds of equal carat weight.

GIA - Diamond Measurements<br>https://www.gia.edu/diamond-shape

Length-to-Width Ratio

The proportion of a fancy shape diamond's length divided by its width, affecting the overall shape and appearance. Each shape has preferred ratio ranges.

GIA - Fancy Shape Proportions<br>https://www.gia.edu/diamond-shape

GIA (Gemological Institute of America)

The world's foremost authority in gemology, established in 1931. GIA created the 4 Cs grading system and provides diamond grading reports.

GIA - About<br>https://www.gia.edu/about-gia

IGI (International Gemological Institute)

An independent gemological laboratory founded in 1975 that provides diamond grading reports, particularly common for lab-grown diamonds.

IGI - About<br>https://www.igi.org/about-igi

Diamond Certificate / Grading Report

An official document from a gemological laboratory (such as GIA or IGI) that details a diamond's characteristics including the 4 Cs, fluorescence, and other identifying features.

GIA - Diamond Reports<br>https://www.gia.edu/report-check-landing

Lab-Grown Diamond

A diamond created in a controlled laboratory environment using technological processes (CVD or HPHT) that replicate natural d