Abrasion: Tiny nicks along facet junctions, producing white fuzzy lines instead of sharp crisp facet edges.

American Gem Society (AGS):An educational institution for gemological studies. The AGS Labs were created primarily to develop and promote universally-accepted standards for grading cut, including Ideal Cut.

Artificial Stone - A gem material that is either a manmade imitation or a synthetic. (See synthetic).

Asterism - The optical phenomenon of seeing a rayed figure in the form of a star. This is caused by the reflection of light from minute oriented and aligned needle-like inclusions.

Baguette: A step cut in the shape of a small rectangular stone. May be tapered at one end.

Baroque - Irregular in shape, such as baroque pearls, tumble-polished stones, or freeform shaped gem materials.

Bearded girdle: Tiny, numerous, hair like fractures extending into the stone.

Bezel: A facet on the Crown, or upper part of the Diamond above the Girdle.

Blemish - Any surface imperfection on the surface of a gemstone. For example, on a diamond, one would be referring to a nick, knot, scratch, abrasion, minor crack or fissure (cavity), or a poor polish.

"Blue-White" - According to the Federal Trade Commission, only diamonds with a distinct blue body color may be traded as "blue-white."  For many years the term referred to a diamond without a distinctive body color, however misuses of this term have rendered it almost meaningless.

Brilliance - Total amount of white light returned to the eye from a diamond or colored stone as the result of internal and external reflections.  The major factors that affect the amount of brilliancy in a gem are refractive index, proportions, polish and transparency.

Brilliant Cut - The most common style of diamond cutting, also used for many other gemstones, which consists of a combination of triangular and kite shaped facets. The round brilliant cut features 57 or 58 facets.

Bort: Industrial grade diamonds Bow-Tie Effect: An effect caused by a shadowy area visible in some fancy shapes, caused by light leaking out the bottom of the Diamond.

Bruise: An inclusions consisting of surface crumbling, often accompanied by tiny, root like feathers.

Burned Facet: This facet may appear whitish, or burnt, as a result of the cutter polishing the facet "against the grain".

Cabochon - An unfaceted cut stone of domed form (having a convex surface). Often called a "cab."

Canary - A term referring to diamonds with an intense yellow hue. The term "fancy yellow" is often used if the yellow makes the stone very distinctive.

Carat - A unit of metric measurement used for gems. One carat (ct.) equals 100 points, 200 milligrams, or 1/5 of a gram.

Carbon Spots: An inaccurate term used by some people in the jewelry industry to describe the appearance of certain inclusions in a diamond. The term refers to included crystals that have a dark appearance, rather than a white or transparent appearance, when viewed under a microscope. In most cases, these dark inclusions are not visible to the naked eye, and do not affect the brilliance of the diamond.

Cavity: An inclusion consisting of a large or deep opening in the stone.

Chance of Color (Color Change) - A phenomenon of some colored stones in which the gem material appears a different color in different types of light. This is caused by selective absorption and/or transmission of the specific type of light to which the gemstone is exposed.

Chip: A tiny piece missing caused by normal wear and tear, or by cutting.

Clarity: A stone's relative position on a flawless to imperfect scale. Clarity characteristics are classified as inclusions (internal) or blemishes (external). The size, number, position, nature, and color or relief of characteristics determine the clarity grade. Very few diamonds are flawless, that is, show no inclusions or blemishes when examined by a skilled grader under 10X magnification. If other factors are equal, flawless stones are most valuable.

Clarity Enhanced - A gemstone that has been treated to improve its appearance by filling fissures or fractures with a transparent substance. Also called "fracture filled."

Clarity Grade - One of the four value factors of a diamond. Diamonds are ranked on a scale from flawless (no inclusions visible under 10x magnification) to included (eye visible inclusions).

Cleavage - The tendency of a crystalline mineral to break in certain definite directions called cleavage planes. The breakage is done by cleaving, a process where a stone is studied so that the plane may be defined and divided with a swift blow. This swift blow splits the stone into proportions quickly as opposed to sawing. 

Cloud: A group of tiny white inclusions which result in a milky or cloudy appearance.

Coated Diamond: A diamond colored by a surface coating which masks the true body-color; the coating may be extensive (entire pavilion, for example), but is more often limited to one or two pavilion facets or a spot on the girdle.

Color: Grading color in the normal range involves deciding how closely a stone's body color approaches colorlessness. Most diamonds have at least a trace of yellow or brown body color. With the exception of some natural fancy colors, such as blue, pink, purple, or red, the colorless grade is the most valuable.

Colored Stone - All natural gemstones except for diamonds or colored diamonds.

Color Grade - One of the four value factors of a diamond. Diamonds are ranked on a scale from "D" (colorless) to "Z" (noticeable tint of color, typically yellow or brown). Diamonds with saturation greater than "Z" color are considered Fancy Colored Diamonds and are graded on a separate scale.

Color Origin - A determination of the cause of color in fancy colored diamonds. Diamonds that are naturally colored are very rare and expensive. Two common ways of enhancing the color of diamonds are irradiation and the high pressure high temperature (HPHT) process.

Crown: The upper part of the diamond above the girdle. Consists of a large flat area on top called a table, and several facets below it. Culet: The smallest facet at the bottom of the diamond.

Crown angle: The angle at which a diamond's bezel facets (or, on emerald cuts, the row of concentric facets) intersect the girdle plane. This gentle slope of the facets that surround the table is what helps to create the dispersion, or fire, in a diamond. White light entering at the different angles in broken up into its spectral hues, creating a beautiful play of color inside the diamond. The crown angle also helps to enhance the brilliance of a diamond.

Culet - The small facet polished across what would otherwise be the sharp point or tip of the pavilion of a faceted stone, especially a round brilliant cut. It is cut and placed with the full intention of avoiding breakage of this tip.

Cut: The proportions and finish of a polished diamond (also called make). Cut can also mean shape, as in emerald cut or marquise cut. Proportions are the size and angle relationships between the facets and different parts of the stone. Finish includes polish and details of facet shape and placement. Cut affects both the weight yield from rough and the optical efficiency of the polished stone; the more successful the cutter is in balancing these considerations, the more valuable the stone will be.

Cultured Pearl- A pearl produced by implanting a shell bead or mantle tissue into the body of a pearl bearing mollusk.  Japan, China, Tahiti, Australia, the U.S., and the Persian Gulf are pearl producing regions.

Depth: The height of a diamond from the culet to the table. The depth is measured in millimeters.

Depth Percentage: On a diamond grading report, you will see two different measurements of the diamond's depth-the actual depth in millimeters (under "measurements" at the top of the report) and the depth percentage, which expresses how deep the diamond is in comparison to how wide it is. This depth percentage of a diamond is important to its brilliance and value, but it only tells part of the story. Where that depth lies is equally important to the diamond's beauty; specifically, the pavilion should be just deep enough to allow light to bounce around inside the diamond and be reflecting out to the eye at the proper angle. Keep in mind, also, that a depth percentage that might be excessive for one diamond cut might be necessary for another type of cut. For example, a 75% or 78% depth in a princess cut diamond would be typical and quite attractive. However, a depth of even 65% would be unnecessary and even detrimental to a round diamond's beauty.

Diamond: A crystal made up of 99.95% pure carbon atoms arranged in an isometric, or cubic, crystal arrangement. It is this unique arrangement of the carbon atoms that makes diamond look and behave differently from other pure carbon minerals such as graphite (the soft black material used to make pencils).

Diamond Cutting: The method by which a rough diamond that has been mined from the earth is shaped into a finished, faceted stone. As a first step, cleaving or sawing is often used to separate the rough into smaller, more workable pieces that will each eventually become an individual polished gem. Next, bruiting grinds away the edges, providing the outline shape (for example, heart, oval or round) for the gem. Faceting is done in two steps: during blocking, the table, culet, bezel and pavilion main facets are cut; afterward, the star, upper girdle and lower girdle facets are added. Once the fully faceted diamond has been inspected and improved, it is boiled in hydrochloric and sulfuric acids to remove dust and oil. The diamond is then considered a finished, polished gem.

Diamond Gauge: An instrument that is used to measure a diamond's length, width and depth in millimeters.

Dispersion - The separation of white light into its component spectral colors (see fire).

Durability - A combination of hardness, toughness and stability that describes a specific gemstone's ability to resist wear.

Emerald Cut - A style of cutting a gemstone in which the outline is a rectangular shape with cut corners and the shape of the facets are rectangular and trapezoid.

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.

Facet: The smooth, flat faces on the surface of a diamond. They allow light to both enter a diamond and reflect off its surface at different angles, creating the wonderful play of color and light for which diamonds are famous. The table below shows all the facets on a round brilliant cut diamond. A round brilliant has 58 facets (or 57 if there is no culet).

Faceted Girdle: Sometimes cutters polish the girdle into 32 facets.

Fancy Diamond: A diamond with an attractive natural body color other than light yellow or light brown

Feathers: These are small fractures in a diamond. They are usually caused by the tremendous stress that the diamond suffered while it was growing underground. In some cases the feather both begins and ends within the diamond's surface and, in other cases, the feather begins inside the diamond and extends to the surface. When viewed under magnification, some feathers are transparent and others have a light white appearance to them. The term "feather" comes from the fact that, under magnification, these fractures often seem to have an indistinct, feathery shape to them. While the idea of buying a diamond with "fractures" may sound scary, the reality is that, with normal wear and care, most feathers pose no risk to the diamond's stability. Consider this: even with the feathers, these diamonds survived their growth and their journey to the surface intact. Once on the surface, they also survived the mining process, as well as the brutal stresses of the diamond cutting process. Though diamonds are certainly not invulnerable to damage, basic consideration to their care and handling during everyday wear will most likely protect them over the course of several human lifetimes.

Flaw: An imperfection of a stone.

Finish - The term referring to the quality of fashioning a gemstone including the polish and symmetry.

Fire - Flashes of spectral colors seen in gemstones as a result of dispersion.

Fluorescence - The process of a material emitting visible light when it is subject to ultraviolet light. For example, diamonds under ultraviolet light will often emit a visible light of a blue hue.

Four C'S - A phrase used to describe a diamond's value characteristics, all starting with the letter "C": cut, color, clarity, and carat weight.

Fracture - A break within a gemstone.

Freshwater Pearl - A pearl that forms in a freshwater living mollusk.

Full Cut Diamond - A description of a brilliant cut, round stone with 57-58 facets.

Gemological Institute of America (GIA): Founded in 1931 by Roger Shipley, this non-profit organization upholds the highest standards for grading diamonds and other precious gems. The GIA has one of the most-respected and well-regarded gemological laboratories in the world; GIA was responsible for developing and standardizing the diamond grading system that is used today by nearly all other gem labs.

Girdle: The outer edge or the widest part of the diamond forming a band around the stone.

Grain Center: A small area of concentrated crystal structure distortion, usually associated with pinpoints.

Hardness: Mineral's resistance to scratching on a smooth surface. Mohs scale of relative hardness consists of 10 minerals, each scratching all those below it in scale and being scratched by all those above it.

Hue: Pure, spectral (prismatic) color. Hues include gradations and mixtures of red, orange, yellow, green, blue, violet and purple.

Included Crystal: A mineral crystal contained in a diamond. Inclusion: Imperfection internal to the Diamond.

Inclusion: A clarity characteristic found within a diamond. Most inclusions were created when the gem first formed in the earth.

Internal Graining: Internal indications of irregular crystal growth. May appear milky, like faint lines or streaks, or may be colored or reflective.

Iridescence - Prismatic colors inside or on the 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.

Irradiated Diamond: A diamond which has been exposed to radiation.

Knot: An included diamond crystal which reaches the surface of a polished diamond.

Laser-Drill Holes: One of the few man-made inclusions that can occur inside a diamond. Why on earth would anyone want to drill holes into a perfectly good diamond? It may seem counter-intuitive, but drilling this type of hole into a diamond can actually raise its clarity grade. In some diamonds, the clarity grade may be determined mainly by the presence of just one or two dark included crystals in a diamond that is otherwise relatively free of inclusions. In certain circumstances, the diamond cutter will decide to use a procedure to remove the dark inclusions and, hopefully, increase the clarity of the diamond.

Loupe: Magnifying glass usually of 10X.

Luster - The quality of reflected and refracted light from the surface of a gemstone or pearl.

Make - Trade term referring to the proportions, symmetry, and polish of a gemstone.

Marquise - A fashioning style for gemstones with the girdle outline in an elliptical shape with pointed ends

Melee - A term used primarily to describe small, round faceted diamonds or colored stones of approximately .18 carat or less.

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) moonstone
7) quartz
8) topaz and beryl
9) corundum
10) diamond

Mounting - Trade term for that portion of a piece of jewelry in which a gem or other object is set.

Nacre - The iridescent substance secreted by a mollusk during the formation of a pearl that consists of layers of aragonite and calcite crystals.

Naturals: Small parts of the original rough diamond's surface which are left on the polished diamond, frequently on or near the girdle. While these are blemishes, they might also be regarded as a sign of skilled cutting; the presence of a natural reflects the cutter's ability to design a beautiful polished gem, while still retaining as much of the original crystal's weight as possible. In many cases, naturals do not affect the clarity grade. In most cases, they are undetectable to the naked eye. Another type of natural is the Indented Natural; in this case, the portion of the original rough diamond's surface which is left on the polished diamond dips slightly inward, creating an indentation. Usually, the cutter makes an effort to cut the polished diamond so that the indented natural will be confined to either the girdle or the pavilion (making it undetectable to the naked eye in the face-up position).

Natural Pearl - A pearl that originates naturally in a mollusk, as distinguished from cultured or imitation pearls.

Needle: A long, thin included crystal which looks like a tiny rod.

Nick: A notch near the girdle or a facet edge.

Off-Make: A poorly proportioned Diamond.

Opaque - A term referring to the transparency of a gemstone; opaque materials do not transmit light.

Orient - The soft iridescent glow on or just below the surface of a pearl or cultured pearl. It is caused by the interference and diffraction of light from the minute crystals comprising the pearl's nacre.

Oval Cut - A fashioning style for gemstones with the girdle outline in an elliptical or oval shape

Pavé: A style of jewelry setting in which numerous small diamonds are mounted close together to create a glistening diamond crust that covers the whole piece of jewelry and obscures the metal under it.

Pavilion: The bottom part of the Diamond, below the girdle.

Pear Shaped Cut - A fashioning style for gemstones with the girdle outline in the shape of a tear drop or pear.

Perfect - The Federal Trade Commission considers it an unfair trade practice to use the word "perfect" or any other word, expression or representation of similar derivative, as a description of any diamond with inclusions that are visible to the naked eye or up to 10X power magnification. This term has been so flagrantly misused in the sale of diamonds that many jewelers avoid its use entirely.

Pinpoints: Miniscule spots internal to a Diamond. A cluster of pinpoints can form a cloud.

Pit: A tiny opening, often looking like a white dot.

Plotting Diagram - A schematic diagram included on the EGL USA Diamond Certificate that illustrates the facets (printed in black) of a diamond and the approximate location and type of internal and external characteristics (printed in red and green).

Point: A unit of measurement used to describe the weight of diamonds. One point is equivalent to one-hundredth of a carat.

Polish: Refers to any blemishes on the surface of the diamond which are not significant enough to affect the clarity grade of the diamond. Examples of blemishes that might be considered as 'polish' characteristics are faint polishing lines and small surface nicks or scratches. Polish is regarded as an indicator of the quality of as diamond's cut; it is graded as either Ideal, Excellent, Very Good, Good, Fair or Poor.

Polished Girdle - A girdle that has been lapped or polished to yield a uniform, highly reflective surface.

Polish Mark: Surface clouding caused by excessive heat (also called burn mark, or burned facet), or uneven polished surface resulting from structural irregularities.

Reflection - The return of light that strikes the surface of stone.

Refraction - The change in direction of a ray of light as it enters a gemstone.

Rough - Any uncut or unpolished gem material.

Rough Girdle: A grainy or pitted girdle surface, often with nicks.

Round Brilliant cut: The most common cut containing 58 facets. Also the most brilliant cut, in terms of most efficient use of light to increase brilliance and fire, hence the name.

Saturation: A color's position on a neutral to vivid scale.

Scintillation - Mirror-like reflections from the facets of a gemstone as it turns in the light.

Scratch: A linear indentation normally seen as a fine white line, curved or straight.

Semi-mount: A jewelry setting that has the side stones already mounted, but which contains an empty set of prongs which are intended to mount a diamond center stone that the customer selects separately.

Simulated Stones - Any substance fashioned to imitate the appearance of a gemstone.

Single Cut - A brilliant cut (round) with 17 or 18 facets: 8 bezel, 8 pavilions, a table and a culet facet.

Solitaire - A term referring to a ring containing a single diamond or other gem.

Star Facets - The eight triangular facets that surround the table facet of a round, brilliant-cut diamond.

Step Cut: One of three styles of faceting arrangements. In this type of arrangement (named because its broad, flat planes resemble stair steps), there are three concentric rows of facets arranged around the table and, on the pavilion, there are three concentric rows arranged around the culet. Other styles of faceting arrangements include the brilliant cut (in which all facets radiate out from the center of the diamond toward its outer edges) and the mixed cut (in which either the crown or pavilion of a diamond is cut as a brilliant cut, and the other part of the diamond is cut as a step cut).

Spread stone: A Diamond with a large table and a thin crown height.

Surface Graining: Surface indication of structural irregularity. May resemble faint facet junction lines, or cause a grooved or wavy surface, often cross facet junctions.

Symmetry - A term referring to the quality of the fashioning of a gemstone. The balance of the outline shape and the precision of the facet arrangement are considered in the symmetry grade

Synthetic - A manmade gem material that has essentially the same physical, optical and chemical properties as that of its natural counterpart.

Table: The flat facet on the top of the diamond. It is the largest facet on a cut diamond.

Table percentage: The value which represents how the diameter of the table facet compares to the diameter of the entire diamond. So, a diamond with a 60% table has a table which is 60% as wide as the diamond's outline. For a round diamond, gemologists calculate table percentage by dividing the diameter of the table, which is measured in millimeters (this millimeter measurement does not appear on diamond grading reports) by the average girdle diameter (an average of the first two millimeter measurements on the top left-hand side of a diamond grading report). For a fancy shape diamond, table percentage is calculated by dividing the width of the table, at the widest part of the diamond, by the millimeter width of the entire stone (this total width measurement is the second of the three millimeter values in the top left-hand corner of the diamond grading report. Contrary to popular misconception, having a small table percentage (53% to 57%) does not make a round diamond any more brilliant than a diamond with a larger table.

Tone: A color's position on a colorless-to-black scale.

Toughness - The ability of a mineral or gemstone to resist breakage (fracturing).  Toughness is not the same as the hardness of a stone.

Transparency - The ability of a substance to transmit light.

Treated Diamonds: A diamond with a body color induced by some form of artificial irradiation, often in conjunction with controlled heating (known as annealing).

Treated Gems - A general term used to describe gemstones that have been artificially modified to improve their color or clarity. Techniques include laser drilling, fracture filling (clarity enhancement), high pressure high temperature (HPHT) annealing, irradiation, and surface coloration.  Gemological laboratories have the equipment and experience to detect the more difficult treatments. 

Trillion - A triangular shaped and faceted gemstone. More specifically, it is a gemstone that has an arched shaped triangle cut with 25 facets on the crown and 19 facets on the pavilion.

Twin Crystals - Two or more mineral crystals that have grown together in a symmetrical nature, usually nonparallel. Sometimes called twinned crystals.

Troy Ounce - A weight unit for precious metals predominately used in England and the U.S.  Twenty pennyweights (dwt) equals one troy ounce, and twelve troy ounces equals one troy pound.

Twinning Wisp: A cloudy area produced by crystal structure distortion, usually associated with twinning planes

Ultrasonic Cleaner - A machine commonly used by jewelers to clean jewelry effectively.  The ultrasonic vibrations free most types of dirt, grime, and oils from the items. Some ultrasonic cleaners come with a heating unit.  When using this type of cleaner, extreme care is recommended because certain gems cannot withstand the heat and vibration.  Consult your professional jeweler.

Ultraviolet Light - Light that is invisible to the naked eye because it consists of wavelengths shorter than those of visible light.

Vermeil - Silver overlaid with gold (gold-plated silver).

White Gold - An alloy of yellow gold that has silver, zinc, or platinum as a whitening agent.

Yellow Gold - The natural color of pure gold as well as the color of karat gold when alloyed with certain metals.