A

ABRASION – Small scratches on the surface of a diamond or colored gemstone. In a diamond, these are usually white in color and caused by contact with other diamonds. See also Plotting Diagram. In a colored gemstone, they are caused by contact with various other materials.

ABSORPTION SPECTRA – A reflection of the electromagnetic radiation absorbed by a colored diamond or colored gemstone over a visible range of wavelengths (approximately 400-800 nanometers). They are recorded on a graph that plots the transmittance against wavelengths. And they can help identify the species and/or variety of stone, as well as the color origin of colored diamonds.

ANNEALING – On a diamond, a controlled temperature process that heats and, then, quickly cools the stone. This treatment is applied individually or in conjunction with high pressure and high temperature (HPHT) and/or irradiation.

ASSEMBLED STONE – A stone consisting of a combination of components held together by bonding material. These components can include natural or synthetic colored gemstones (of similar or mixed variety), glass, and/or other manufactured products.

ASTERISM – An optical phenomenon in which star-like rays are visible in a colored gemstone. This is caused by the reflection of light from minute, oriented, and aligned needle-like inclusions.

 

B

BAGUETTE – A rectangular style of step cut used for diamonds and colored gemstones.

BAROQUE – Irregular and/or non-symmetrical in shape, such as baroque pearls.

BI-COLORATION – A phenomenon in which two colors are visible in a colored gemstone.

BLEACHING – A topical treatment, typically using acids or hydrogen peroxide, that lightens and/or evens out hue. Bleaching is used on select colored gemstones, including jadeite and coral, and pearls.

BLEMISH – A surface feature on the exterior of a diamond or colored gemstone, such as an abrasion, natural, nick, or scratch. A blemish can affect the finish of a stone. For diamonds, see also Plotting Diagram.

BRILLIANCE – The overall strength of a diamond’s light return, an average measured in the face-up position. See also Light Performance.

BRILLIANT CUT – The most common style of diamond cutting, also used for some colored gemstones, traditionally consisting of a combination of triangular, octagonal, and kite-shaped facets. See also Cut (Shape and Style).

BRUISE – A minute imperfection that breaks the surface of a diamond or colored gemstone. For diamonds, see also Plotting Diagram.

BRUTED GIRDLE – On a diamond or colored gemstone, a girdle that is cut, but unpolished.

 

C

CABOCHON – A polished cut colored gemstone of domed form (having a convex surface). See also Cut (Shape and Style).

CARAT WEIGHT – A unit of metric measurement used for diamonds and colored gemstones. One carat (ct.) equals 100 points, 200 milligrams, or 1/5 of a gram. The chart below illustrates carat weights for diamonds.

CAVITY – An isolated opening that breaks the surface of a diamond or colored gemstone. For diamonds, see also Plotting Diagram.

CHATOYANCY – An optical phenomenon, also known as the Cat’s Eye effect, in which a narrow band or line resembling a cat’s eye is visible in a cabochon-cut colored gemstone. This is caused by the reflection of light from minute (typically parallel) inclusions.

CHEMICAL VAPOR DEPOSITION (CVD) DIAMOND – See Lab-Grown Diamond.

CHIP – A shallow, jagged surface break on a diamond or colored gemstone. For diamonds, see also Plotting Diagram.

CLARITY GRADE – A scale that considers blemishes and inclusions, to rank diamonds from FL (flawless) to I (included). The scale is divided into 12 sub-grades, as detailed below:

   

CLEAVAGE – A major fracture or weak point in a diamond that is breakable in certain definite planes or directions, usually due to weak molecular bonding. On an EGL USA report, it would be noted as an extended version of a feather symbol. See also Plotting Diagram.

CLOUD – In a diamond or colored gemstone, a cloud-like, semi-transparent area created by minute pinpoint inclusions. On EGL USA reports, it is plotted for diamonds (see also Plotting Diagram) and noted for colored gemstones.

COLOR CHANGE (CHANGE OF COLOR) – In some diamonds, known as chameleons, a phenomenon in which their color changes when exposed to certain intensities of heat or when kept in darkness for an extended period of time. In some colored gemstones, a phenomenon in which their hue appears to vary when exposed to different types of light.

COLORED DIAMONDS – See Color Grade.

COLOR DISTRIBUTION – An assessment of the homogeneity of color in a colored diamond, as seen through its crown. It is measured on a scale ranging from uneven to even (which is preferred).

COLOR GRADE – A scale that identifies diamonds or colored diamonds according to color.

For colorless to light diamonds, color is graded on a scale from “D” (colorless) to “Z” (possessing a strong tonal modifier, such as brown, gray, green, pink, or yellow.) The chart below depicts the most typical modifier: yellow.

   

Colored diamonds are distinguished by a combination of hue, tone, and saturation. Fancy colored diamonds are graded on a scale from fancy light to fancy vivid. Colored diamonds outside of the fancy range are rated as faint to light. While remarkable diamonds exist in many colors, natural fancy vivids are typically the most rare and valuable. The chart below depicts these variations for a yellow diamond.

COLOR ORIGIN – For a colored diamond, the basis of its color. This can include foundations described as natural, enhanced, high pressure and high temperature (HPHT)-treated, etc.

COLOR/OVERTONE – In reference to pearls, the main color or body color can be white, cream, gray, black, yellow, etc. Often, a pearl will also display an overtone: a translucent secondary color on its surface. Beautiful pearls can be found in virtually any color/overtone.

COLORED DIAMOND – A diamond distinguished by a combination of hue, tone, and saturation. See also Color Grade.

COLORED GEMSTONE – A gemstone distinguished by its hue or by a combination of hue, tone, and saturation. Typically, colored gemstones exhibit single colors. More unique phenomena — such as bi-coloration, color-change, play of color, asterism, or chatoyancy — can create distinctive stones.

COMPOSITE STONE – A stone created from a minimal amount of natural or synthetic colored gemstones mixed with other manufactured products. The resulting stone, typically, has the appearance of a colored gemstone, with very little actual colored gemstone content.

CONFLICT DIAMOND – A diamond (also known as a blood diamond) mined to fund violent conflict and/or civil war against a legitimate government. Such mining is, typically, also linked to dire human rights abuses. Blood diamonds have originated in Africa: Angola, the Central African Republic, Côte d’Ivoire, the Democratic Republic of the Congo (DRC), Liberia, the Republic of Congo, and Sierra Leone. It should be noted, that the amount of conflict diamonds as a percentage of world diamond production has fallen dramatically, currently resting at about 4 percent. In countries where legislation is in place prohibiting the sale of conflict diamonds, the percentages are much lower. See also Kimberley Process.

CONTRAST – The intensity of a diamond’s brightness, a ratio of the brightest pixels compared to all of the pixels in a face-up view of the stone. See also Light Performance.

COUNTRY OF ORIGIN – The presumed geographical source of a colored gemstone, discoverable only for particular stones with unique identifying characteristics.

CROWN – The part of any faceted diamond or colored gemstone above the girdle. See also Proportions.

CRYSTAL – For a diamond or colored gemstone, a visible crystalline structure of variable transparency on the interior of the stone. This can occur naturally or as a result of a treatment, and typically serves as an identifying characteristic. On EGL USA reports, it is plotted for diamonds (see also Plotting Diagram) and noted as an identifying characteristic for colored gemstones.

CRYSTAL WITH HALO – On a colored gemstone, a cloudy, irregular feature with a glowing border, created when a crystal bursts during heat treatment. A crystal with halo can be an identifying characteristic noted on an EGL USA report.

CULET – The small facet polished across what would otherwise be the sharp point or tip of the pavilion of a faceted diamond or colored gemstone. This is described on a range from none (a sharp point) to extremely large (an extended, flatter surface). For diamonds, see also Proportions.

CULTURED PEARL – A pearl initiated by the implantation of a nucleus (a shell bead or piece of mantle tissue) by a pearl farmer. Although they are more common than natural pearls, cultured pearls — such as the classic South Sea, lustrous Akoya, and colorful Tahitian — can be quite stunning.

Typical Cultured Pearl

   

Non-Nacre Body

Nacre Coating

CUSHION CUT – A diamond or colored gemstone shape in which the outline is square or rectangular, with rounded corners and/or bowed sides. See also Cut (Shape and Style).

CUT (SHAPE AND STYLE) – A description of the silhouette or form created by the contours and facets of a diamond or colored gemstone. Shapes vary from round to fancy cuts, such as cushion, emerald, heart, marquise, oval, pear, princess, and triangle. And style includes variations of brilliant, step, mixed, and, for colored gemstones, cabochon cuts. Beautiful stones can be found in virtually any shape or style.

Sample Shapes

   

CUSHION

EMERALD

HEART

MARQUISE

OVAL

PEAR

PRINCESS

ROUND

TRIANGLE

Sample Styles

   

 

Top (Crown) View      Side (Pavilion) View

BRILLIANT

STEP

MIXED

CABOCHON

CUT GRADE – A ranking based on the combined analysis of a diamond’s proportions, polish, and symmetry — factors that determine the way light interacts with the stone. On an EGL USA Cut Grade Diamond Report, most preferred stones are graded on a scale from very good to ideal plus, as noted below.

IDEAL PLUS

IDEAL

VERY GOOD

ROUND

PRINCESS

 

D

DIAMOND – A mineral that crystallizes in the cubic system and is composed of carbon with a hardness of 10 (the hardest of all naturally occurring substances on the Mohs Scale), a refractive index of 2.417, and a specific gravity of 3.52. Diamonds are sub-classified into types (I and II) that distinguish and identify the concentration and location of nitrogen in their crystalline structure.

DIAMOND’S NATURAL ATTRACTION (DNA)™ – EGL USA’s scientific assessment of a diamond’s visual appeal. Twelve criteria — traditional measurements and innovative light performance evaluations — are considered. These are table and depth percentage; pavilion angle and percentage; crown angle and height; culet size; girdle thickness; finish; brilliance; contrast; and radiance. DNA™ is rated on a scale from poor to excellent plus. And it is part of the advanced analysis available exclusively in EGL USA’s 360° Diamond Report™. See also Light Performance.

DIFFUSION – On a colored gemstone, the introduction of chemicals combined with high temperatures to create color enhancing or asterism effects. Diffusion can impact color throughout a gem or merely on its surface. Like other surface treatments, the latter tends to be less permanent. Diffusion is used on stones such as feldspars, rubies, and sapphires.

DISPERSION – The separation of white light into its component spectral colors. See also Fire.

DURABILITY – A combination of hardness, toughness, and stability that describes the ability of a specific diamond or colored gemstone to resist wear.

DYEING – On a colored gemstone, the application of coloring agents to alter, intensify, or improve consistency of hue. In pearls, the use of chemicals or dyes to change the nacre’s color or overtone. The results of this process can range from distinct color transformations to subtle overtone shifts. EGL USA reports clearly identify dyed colored gemstones and pearls.

 

E

EMERALD CUT – A diamond or colored gemstone shape in which the outline is rectangular with cut corners, and the facets are rectangular and trapezoidal. See also Cut (Shape and Style).

ENAMEL – A vitreous glaze. In jewelry, it is usually fused glass that is heated to a base — most commonly to the surface of metal, glass, or pottery.

ENVIRONMENT – For pearls, the original setting for growth: freshwater or saltwater.

EXTRA FACET – An additional small, flat surface on a diamond or colored gemstone. For diamonds, see also Plotting Diagram.

 

F

FACET – One of the small, flat surfaces that is polished on a diamond or colored gemstone.

FACETED GIRDLE – On a diamond or colored gemstone, a girdle that is cut and polished for maximum surface reflection, with many flat planes around the circumference of the stone.

FANCY COLOR – See Color Grade.

FANCY CUT – A diamond or colored gemstone shape other than round. See also Cut (Shape and Style).

FEATHER – A fracture in a diamond or colored gemstone that typically breaks the surface. For diamonds, see also Plotting Diagram.

FEATHER FILLING – Also known as fracture filling, a treatment that introduces a glass-like material in the natural feathers or fractures of a diamond or colored gemstone.

For diamonds, this process enhances the appearance of clarity. While the treatment is stable for normal wear, it is not considered permanent. In most cases, should damage to the treatment occur, the diamond can be repaired and its enhancement restored. EGL USA clearly identifies such stones with laser inscriptions, along with special Enhanced Diamond Reports. For diamonds, see also Plotting Diagram.

For colored gemstones — such as alexandrites, emeralds, rubies, and tourmalines — feather filling can also enhance the appearance of clarity. In addition, it can improve durability.

FINGERPRINT – An identifying characteristic in a diamond or colored gemstone, similar in appearance to a feather.

FINISH – The analysis of a diamond’s polish and symmetry. Polish relates directly to the quality of the overall surface condition of the diamond. Symmetry relates to facet shape and arrangement, and the overall exactness of the stone’s contour and outline. Both are rated on a scale ranging from poor to excellent.

FIRE – Flashes of rainbow or spectral colors seen in diamonds or colored gemstones as a result of dispersion.

FL (FLAWLESS) GRADE – See Clarity Grade.

FLUORESCENCE – The capacity of diamonds, colored gemstones, and pearls to emit visible light when exposed to higher energy wavelengths. In diamonds and colored gemstones, this occurs when their atoms react to long- and short-wave ultraviolet rays. In pearls, this occurs when some of their elements react to x-rays. Fluorescence is measured for identification purposes and described on a scale from inert (none) to very strong. Its presence can also help to confirm a pearl’s cultured origin.

FOUR CS – An industry phrase used to describe a diamond’s characteristics, all starting with the letter "C": carat weight, clarity, color, and cut.

FRACTURE FILLING – See Feather Filling.

FULL CUT – A description of a brilliant cut, round diamond or colored gemstone with 57-58 facets.

 

G

GEMSTONE – A mineral, rock, organic, or inorganic material that is, typically, cut and polished for use in jewelry. There are dozens of types of gemstones — including diamonds, colored gemstones, and pearls — each with a unique set of physical and optical properties.

GIRDLE – The narrow band around the perimeter of a polished or faceted diamond or colored gemstone. A girdle separates the crown from the pavilion facets and will vary in thickness depending on a stone’s individual style and shape. Thickness is measured on a scale from extremely thin to extremely thick, with mid-range thickness being preferred. A girdle can be further described as bruted, faceted, polished, or a combination of these. See also Proportions.

GRAINING – Lines or patterns visible at the juncture between two crystals, formed either on the surface or within a diamond or colored gemstone. On EGL USA reports, it is plotted for diamonds (see also Plotting Diagram) and noted for colored gemstones.

GRAINS – For pearls, a unit of weight measurement equivalent to .065 gram. Depending on pearl type, weight can be measured in grams, carats (.2 gram), or grains.

 

H

HARDNESS – The ability of a diamond or colored gemstone to resist scratching. A diamond is the hardest specimen in nature. See also Mohs Scale.

HEART CUT – A diamond or colored gemstone shape in which the outline is like its name: heart-shaped. See also Cut (Shape and Style).

HEARTS & ARROWS CUT – A precise diamond cut that creates a unique, romantic facet pattern. Viewed through its pavilion, the stone shows a circle of hearts. And through its crown, it reveals arrows. On an EGL USA Hearts & Arrows Diamond Report, cut is rated on a scale from very good to ideal plus (the most symmetrical). The diagram below depicts a symmetrical hearts & arrows cut.

       Pavilion View                Crown View

HEATING – On a colored gemstone, the application of controlled high temperatures to alter or improve its color and/or internal structure. Heat enhances many types of gemstones. And it achieves this by essentially continuing the process started by nature. For example, heat can turn a naturally brown tanzanite into a striking blue/violet, or transform a cloudy ruby to a distinct red. Pearls can also be treated with high temperatures to modify color. However, heat is often used with other treatments, such as bleaching, to maximize effects.

HIGH PRESSURE AND HIGH TEMPERATURE (HPHT) – For diamonds, a treatment that applies extreme pressure and temperature to cause the addition or deletion of color. HPHT can transform pale diamonds into vibrant fancy colors. And it can shift brown-toned diamonds to more delicate hues such as colorless, near colorless, pink, yellow, yellow/orange, orange, and green/yellow. EGL USA clearly identifies HPHT-treated stones with laser inscriptions.

HIGH PRESSURE AND HIGH TEMPERATURE (HPHT) DIAMOND – See Lab-Grown Diamond.

HUE – The primary impression of color such as red, green, or blue.

 

I

I (INCLUDED) GRADE – See Clarity Grade.

IDEAL CUT DIAMOND – A diamond with exceptional cut grade quality, ranked by a combined analysis of its proportions, polish, and symmetry. See also Cut Grade.

IDENTIFYING CHARACTERISTICS – Physical aspects of a diamond or colored gemstone that help to confirm its singularity or categorization. These can range from inclusions (fingerprints, needles, etc.) to modifiers caused by treatments (crystals with halos, reduced silks, etc.). In addition, identifying characteristics can refer to instrument-based measurements such as refractive index, x-ray fluorescence, infrared spectra, Raman spectra, or specific gravity.

IF (INTERNALLY FLAWLESS) GRADE – See Clarity Grade.

IMPREGNATION – The application of a colorless agent — such as wax, oil, resin, or other polymer material — into a porous colored gemstone. Impregnation is used to improve the durability and appearance of stones such as jades, opals, and turquoises.

INCLUSION – An internal feature on a diamond or a colored gemstone, such as a cavity, crystal, feather, internal graining, pinpoint, etc. On EGL USA reports, it is plotted for diamonds (see also Plotting Diagram) and, when serving as an identifying characteristic, noted for colored gemstones.

INDENTED NATURAL – A portion of the original surface of a rough diamond left by the cutter when polishing and faceting a diamond. Indented naturals are usually on the girdle and break the outline of the stone.

INFRARED LIGHT – Part of the electromagnetic spectrum that is not visible to the human eye, between approximately 800 nanometers (longer than red in the visible spectrum) to 1 millimeter (bordering microwave).

INFRARED SPECTRA – A representation of the vibrational modes of a diamond’s or colored gemstone’s molecules over a range of wavelengths outside of the visible spectrum. They are recorded on a graph that plots intensity against wavelengths. And they can help identify the species and/or variety of stone.

INTERNAL GRAINING – See Graining.

INTERNAL LASER DRILL – In a diamond, a flat channel-like feature created by a laser beam during the treatment of an included crystal. The internal laser drill extends from the inclusion to the stone’s surface, where it appears as a linear feature. See also Plotting Diagram.

INTERNAL LASER DRILLING – A diamond treatment, also called Kiduah Meyuhad (KM) or “special drill” in Hebrew, in which a laser beam is focused directly on an inclusion to create a feather-like fracture between the inclusion and the stone’s surface. The inclusion is then treated with acid to improve the perceived clarity of the stone. This type of laser drilling is, typically, more challenging to detect than traditional laser drilling. On an EGL USA report, internal laser drilling is clearly noted.

IRIDESCENCE – Prismatic colors on the inside or surface of a material, caused by light interference from thin layers of differing refractive indices. These layers may be thin films of liquid, gas, or solid. Pearls are best known for exhibiting iridescence.

IRRADIATION – The use of radiation to alter the appearance of a diamond, colored gemstone, or pearl. On a diamond or colored gemstone, radiation such as neutron or electron bombardment can change the internal structure and, therefore, the stone’s color and perceived clarity. This process is often followed by heating, which can further refine the results. Irradiation can create vibrant pink, yellow, green, and green/blue hues in diamonds, as well as beautiful blue topazes and red tourmalines. On certain pearls, such as freshwater or Akoya pearls, gamma ray treatments can generate darker gray, blue, or black colors.

 

K

KARAT – A measure of the purity of gold. Pure or fine gold is 24 karat (24K). Pure gold is quite soft, so it is typically mixed with other metal(s) to make jewelry. Other karat designations indicate the proportions of 24 parts of the mixture:

18K is 18 parts fine gold and 6 parts metal(s), or a total of 75% pure gold;
14K is 14 parts fine gold and 10 parts metal(s) or a total of 58.3% pure gold; and
10K is 10 parts fine gold and 14 parts metal(s) or a total of 41.7% pure gold.

Jewelry is stamped to indicate karat value (i.e. “750” or “18K” for 18 karat; “585” or “14K” for 14 karat).

KIMBERLEY PROCESS (KP) – An international certification scheme that establishes requirements for the production and trade of rough diamonds. The process aims to prevent the flow of conflict diamonds, while helping to protect legitimate trade in rough diamonds (which are certified as “conflict-free”). As of August 2012, KP had 51 participants representing 77 countries. A 2006 review of the process confirmed its effectiveness, but recommended strengthening aspects such as the monitoring of implementation and internal controls in participating countries, as well as greater transparency in the gathering of statistical data. A mandated review of the core objectives, core definitions, and functioning of KP is set to occur during 2012-2013.

KNOT – In a diamond, an included crystal that extends to the surface. See also Plotting Diagram.

 

L

LAB-GROWN DIAMOND – A man-made stone (also known as synthetic) typically created through high pressure and high temperature (HPHT) or chemical vapor deposition (CVD). Unlike simulated diamonds (such as cubic zirconia), which merely look like diamonds, lab-grown diamonds have essentially the same chemical, physical, and optical properties as natural diamonds. EGL USA identifies lab-grown diamonds with laser inscriptions and special
Lab-Grown Diamond Reports.

LASER DRILL HOLE – A minute channel from a diamond’s surface to its interior, created by a laser beam during the treatment of an included crystal. See also Plotting Diagram.

LASER DRILLING – A diamond treatment in which a laser beam creates a channel to allow access to a dark inclusion. The inclusion is then lightened with acid, to improve the perceived clarity of the stone. On an EGL USA report, laser drilling is clearly noted.

LEAKAGE – A phenomenon that occurs in diamonds and colored gemstones when light entering a stone fails to reflect back through its crown, dispersing instead through the pavilion.

LIGHT PERFORMANCE – The combined impact of brilliance, contrast, and radiance of a diamond as seen by the human eye under normal lighting conditions. These terms are defined and their impact is measured by a light behavior assessment system. On an EGL USA 360° Diamond Report™, each aspect is rated on a scale from poor to excellent. Superior performance in any of the three categories can yield a beautiful stone.

LUSTER – On a pearl, the reflective quality or brilliance of the surface, measured on a scale ranging from poor to excellent.

 

M

MARQUISE CUT – A diamond or colored gemstone shape in which the girdle outline is elliptical, with pointed ends. See also Cut (Shape and Style).

MATCHING – In pearl strands or jewelry, the coordination of the pearls — in aspects such as color and shape — to create an aesthetically pleasing piece. It is described on a scale from poor to excellent.

MEASUREMENTS – For round diamonds and colored gemstones, an indication of maximum-minimum diameter x depth, in millimeters. Fancy shapes are indicated by length x width x depth. For round pearls, an indication of diameter, in millimeters. Other pearls are measured by length x width x depth. Measurements of pearl strands or jewelry are described as a range, average, or graduation from maximum to minimum.

MELEE – A term used primarily to describe small faceted diamonds or colored gemstones of approximately .12 carat or less.

MIXED CUT – A style of diamond or colored gemstone cutting that features aspects of both brilliant and step cutting. See also Cut (Shape and Style).

MOHS SCALE – A loose scale of hardness, used for field collecting, which allows for identification of specimens. Devised by Friedrich Mohs, a German mineralogist, in the 19th century. The comparative scale of hardness is as follows:

1)    Talc
2)    Gypsum
3)    Calcite
4)    Fluorite
5)    Apatite
6)    Feldspar
7)    Quartz
8)    Topaz and Beryl
9)    Corundum
10)  Diamond

MOUNTING – The portion of a piece of jewelry in which a gemstone or other object is set.

 

N

NACRE – The iridescent coating over a pearl’s nucleus. Its depth can impact the pearl’s luster, durability, and quality. On bead-cultured pearls, thickness is rated as thin, medium, or thick (which is preferred).

NACREOUS PEARL – A pearl that appears translucent, due to its fine, plate-like crystalline layers of calcium carbonate (mostly aragonite) and organic material (conchiolin).

NATURAL – A portion of the original surface of a rough diamond left by the cutter when polishing and faceting a diamond. Naturals are usually near the girdle of a diamond. See also Plotting Diagram.

NATURAL PEARL – A pearl created when nacre forms around a microscopic irritant, without human interaction. Such pearls are often coveted for their rarity (as opposed to more commonly available cultured pearls.)

Typical Natural Pearl

   

Nacre Body

NEEDLE – A thin inclusion of variable length, in a diamond or colored gemstone. On EGL USA reports, it is plotted for diamonds (see also Plotting Diagram) and noted as an identifying characteristic for colored gemstones.

NICK – A minor chip on the surface of a diamond, usually found near or on the girdle of the stone. See also Plotting Diagram.

NON-NACREOUS PEARL – A pearl made of coarser crystals (mostly calcite), resulting in a more porcelain-like look than that of a nacreous pearl. Examples include a conch or melo pearl.

 

O

OPAQUE – A description of a characteristic of a diamond or colored gemstone that is neither transparent nor translucent, so it does not transmit light.

ORIENT – On a pearl, the soft iridescent glow on or just below the surface. It is caused by the interference and diffraction of light from the minute crystals comprising the nacre.

OVAL CUT – A diamond or colored gemstone shape in which the girdle outline is elliptical or oval. See also Cut (Shape and Style).

OVERTONE – See Color/Overtone.

 

P

PAVILION – The portion of a faceted diamond or colored gemstone that lies below the girdle. See also Proportions.

PEAR CUT – A diamond or colored gemstone shape in which the girdle outline is teardrop- or pear-shaped. See also Cut (Shape and Style).

PEARL – See Cultured Pearl, Nacreous Pearl, Natural Pearl, and Non-Nacreous Pearl.

PHOSPHORESCENCE – The capacity of a diamond or colored gemstone to emit visible light for a variable period of time after exposure to long- and short-wave ultraviolet rays.

PINPOINT – Inside a diamond or colored gemstone, a minute, circular inclusion. On EGL USA reports, it is plotted for diamonds (see also Plotting Diagram) and noted for gemstones.

PIT – On a diamond’s surface, a miniscule indentation. See also Plotting Diagram.

PLATINUM – A rare, white metal, known for its bright color and great durability. Platinum belongs to the platinum group of metals, or PGMs: platinum, iridium, palladium, ruthenium, rhodium, and osmium. Platinum is typically used in almost pure form (95% platinum, 5% other metals). So, it has the added benefit of being hypoallergenic. Such jewelry is identified with an engraved mark of “platinum.” Jewelry that uses less pure platinum is marked numerically (i.e. “850 Plat,” for 85% platinum).

PLAY OF COLOR – In a colored gemstone, a phenomenon in which its color appears to flash or change as the stone is tilted. This is caused by diffraction and can be seen most easily in opals.

PLOTTING DIAGRAM – A schematic diagram that approximates a diamond’s style and shape, and notes its external and internal characteristics. On an EGL USA report, the facets are printed in black and the characteristics are denoted in red and green, by the symbols below.

External Characteristics                          Internal Characteristics

   

Abrasion
Extra Facet
Natural
Nick

Pit
Polish Lines
Scratch
Surface Grinding

Bruise
Cavity
Chip
Cloud
Crystal
Feather
Feather Filled
Indented Natural

Internal Graining
Internal Laser Drill
Knot
Laser Drill Hole
Needle
Pinpoint
Twinning Wisp

   

Sample Plotting Diagram

   

POINT – A measurement in the weight of a diamond or colored gemstone equal to 1/100 of a carat. Thus, 0.50 carats is equal to 50 points.

POLISH – See Finish.

POLISH LINES – Small parallel lines left on the surface of a diamond’s or colored gemstone’s facets by a rotating polishing/grinding wheel. For diamonds, see also Plotting Diagram.

POLISHED GIRDLE – On a diamond or colored gemstone, a girdle that has been cut and polished to yield a uniform, highly reflective surface. See also Girdle.

PRINCESS CUT – A diamond or colored gemstone shape in which the outline is either square or rectangular, with pointed corners. See also Cut (Shape and Style).

PROPORTIONS – On a diamond or colored gemstone, the dimensions and facet angles, and the relationship between them. On EGL USA diamond reports, proportions are noted or diagrammed. See also Measurements.

Diameter
Table

Crown Angle
Pavilion Angle

Crown

Girdle

Depth

Pavilion

Culet

 

R

RADIANCE – The amount of reflected and refracted light in a diamond, sometimes referred to as sparkle or life, measured in a face-up view. See also Light Performance.

RAMAN SPECTRA – A representation of the vibrational modes of a diamond’s, colored gemstone’s, or pearl’s molecules as they react to a monochromatic (laser) light source. For diamonds, the Raman spectra measure photo luminescence to detect treatments to the stone. For all stones, Raman spectra are recorded on a graph that plots intensity versus frequency. And they can help identify the species and/or variety of stone, as well as any applied treatments.

REDUCED SILK – A structurally changed needle, caused by heat treatment in a colored gemstone. On an EGL USA report, this is noted as an identifying characteristic.

REFLECTION – The return of light that strikes the surface of a diamond or colored gemstone. This effect can also occur when light strikes specific inclusions within a stone.

REFRACTION – The change in direction of a ray of light as it enters a diamond or colored gemstone.

REFRACTIVE INDEX – The degree to which visible light bends as it passes through a diamond, colored gemstone, or pearl. Each type of gemstone exhibits a unique refractive index (RI) or RI range — a result of its distinct chemical composition and physical crystallization. As such, RI is a strong identifying characteristic.

ROSE GOLD – Also known as pink gold, an alloy of yellow gold mixed with copper.

ROUGH – Any uncut or unpolished diamond or colored gemstone.

ROUND CUT – A diamond or colored gemstone shape in which the outline is circular. See also Cut (Shape and Style).

 

S

SATURATION – An attribute of color that denotes its strength.

SCINTILLATION – Mirror-like reflections from the facets of a diamond as it turns in the light.

SCRATCH – On the surface of a diamond or colored gemstone, a white, narrow, shallow marked caused by abrasion. For diamonds, see also Plotting Diagram.

SHAPE OF COLORED GEMSTONES – See Cut (Shape and Style).

SHAPE OF DIAMONDS – See Cut (Shape and Style).

SHAPE OF PEARLS – A variety of forms that includes round, off-round, oval, drop (pear-shaped), button (with a flat side), circle (with rings/ridges), and baroque (irregular and/or non-symmetrical).

ROUND

OFF-ROUND

OVAL

DROP

BUTTON

CIRCLE

BAROQUE

SI (SLIGHTLY INCLUDED) GRADE – See Clarity Grade.

SILK – A naturally occurring, short needle in a colored gemstone. On an EGL USA report, this is noted as an identifying characteristic.

SIMULATED DIAMOND – An imitation diamond, such as cubic zirconia, that looks like a diamond, but does not share its combination of chemical, physical, and optical properties.

SINGLE CUT – Traditionally, a round cut for a diamond or colored gemstone with 17 facets: nine crown facets (including the table) and eight pavilion facets.

SOLITAIRE – A piece of jewelry containing a single diamond or colored gemstone.

SPECIES – A group of gemstones that share similar chemical composition and physical structure. Examples of species include beryl and corundum. See also Variety.

SPECIFIC GRAVITY – The ratio of the density of a solid or liquid to the density of an equal volume of water (or for a gas, to an equal volume of hydrogen).

STABILITY – Ability of a diamond or colored gemstone to maintain its integrity under normal conditions.

STEP CUT – A style of diamond- or colored gemstone-cutting that creates straight facets that run parallel to the girdle and decrease in size as they move further from it (resembling steps), as in an emerald cut. See also Cut (Shape and Style).

STERLING SILVER – An alloy of 92.5% silver and 7.5% of another metal, usually copper, nickel, or zinc. The addition of the second metal, balances the softness of the pure (or fine) silver. Sterling silver pieces are engraved with identifying marks, such as “sterling” or “.925.”

SURFACE COATING – On a diamond, colored gemstone, or pearl, the application of a thin artificial layer on the stone’s exterior to impact appearance. Coatings are, typically, not considered permanent; their effects may diminish over time.

On a diamond, chemical coatings can disguise less desirable interior hues. On a colored gemstone, coatings can improve color and overall appearance. And on a pearl, coatings can create the illusion of a smoother surface and/or enhanced luster. On an EGL USA report for any stone type, coatings are clearly noted. In addition, EGL USA does not provide color or clarity grades for coated diamonds.

SURFACE GRAINING – See Graining.

SUSTAINABLE ORIGIN – Sustainable origin refers to the environmentally-friendly source of a diamond or colored gemstone and, if applicable, its related jewelry material. This can include heirloom and reclaimed items, as well as newly mined items that are conflict-free and ethically-sourced.

SYMMETRY – See Finish.

SYNTHETIC COLORED GEMSTONE – A man-made stone created through various processes. Synthetic colored gemstones have essentially the same chemical, physical, and optical properties as natural colored gemstones.

 

T

TABLE – The horizontal, top flat facet on the crown of a faceted diamond or colored gemstone. See also Proportions.

TONE – An attribute of color that denotes its lightness or darkness.

TOUGHNESS – The ability of a mineral or gemstone to resist breakage. Jadeite is the toughest gemstone due to an interlocking molecular structure that helps to minimize its weak points.

TRANSPARENCY – The amount of light transmitted through a diamond or colored gemstone. It is influenced by the texture of the material itself and the presence of inclusions. Transparency is rated on a scale of transparent (typically preferred), semi-transparent, translucent, semi-translucent, and opaque.

TREATMENT – The application of processes or agents to enhance the perceived color, clarity, phenomena, or durability of a diamond, colored gemstone, or pearl. Treatments are routinely applied to stones, with measurable results. Treatments are disclosed on EGL USA reports.

For diamonds, see also Annealing, Feather Filling, High Pressure and High Temperature (HPHT), Irradiation, Internal Laser Drilling, Laser Drilling, and Surface Coating.

For colored gemstones, see also Bleaching, Diffusion, Dyeing, Feather Filling, Heating, Impregnation, Infusion, Irradiation, and Surface Coating.

For pearls, see also Bleaching, Dyeing, Heating, Irradiation, and Surface Coating.

TRIANGLE CUT – A three-sided diamond or colored gemstone shape in which the outline is like its name: triangular. See also Cut (Shape and Style).

TROY OUNCE – A unique weight unit for precious metals, including gold, silver, and platinum. Although it is similar in name, a troy ounce is actually heavier than an “ordinary” (avoirdupois) ounce. One troy ounce is equivalent to approximately 1.097 ordinary ounces or 31.1 grams. And it has its own internal weight system: Twenty pennyweights (dwt) equal one troy ounce, and twelve troy ounces equal one troy pound.

TWINNING WISP – Inside a diamond, an irregular ribbon-like pattern. See also Plotting Diagram.

 

U

ULTRAVIOLET LIGHT – Light that is invisible to the naked eye because it consists of wavelengths shorter than those of visible light.

 

V

VARIETY – A subcategory of species, used to further define stones based on common color or phenomena. The beryl species, for example, includes emerald and aquamarine varieties. And corundum includes ruby and sapphire varieties. See also Species.

VS (VERY SLIGHTLY INCLUDED) GRADE – See Clarity Grade.

VVS (VERY VERY SLIGHTLY INCLUDED) GRADE – See Clarity Grade.

 

W

WHITE GOLD – An alloy of yellow gold that contains copper, with nickel, silver, or zinc as a whitening agent.

WISP – A curvy, hair-like feature on a diamond or colored gemstone that can appear as an isolated element or in a cloud-like form.

 

X

X-RAY FLUORESCENCE – Also known as XRF, the capacity of a diamond, colored gemstone, or pearl to emit energy via secondary x-rays when exposed to a high-energy incident (primary) x-ray. The intensity of the emitted x-rays indicates the stone’s chemical elements for identification purposes.

 

Y

YELLOW GOLD – The natural color of pure gold, as well as the color of gold when alloyed with certain metals.

Note: All photos and diagrams above are intended as general guides.
Renderings may vary with computer settings.