Glossary of Terms

Glossary For Colored Gemstones and Diamonds

A, B, C, D, E, F, G, H, I, K, L, M, N, O, P, R, S, T, U, V, W, X, Y, Z


AMERICAN CUT - First designed by Marcel Tolkowsky, this type of cut is also called an Ideal cut. Tolkowsky used mathematics to calculate the proper proportion to increase a diamond's brilliancy (fire) when cut in a round shape.

ARTIFICIAL STONE - A gem material which 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 - Rectangular style of step cut used for small gem materials.

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

BEAD - A spherical object, with or without facets, distinguished by a hole drilled through the stone, usually on center.

BIWA PEARL - A mantle-tissue, nucleated, freshwater cultured pearl from Lake Biwa, Japan. Properly called a freshwater pearl.

BLEMISH - Any surface imperfection within or on 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 DIAMOND - A diamond with a distinctly blue body color, even if very light in tone. This type of diamond is considered a "fancy" diamond. (Note: Diamonds can have blue tonal hues artificially added such as with color enhanced diamonds).

"BLUE-WHITE" - A term used for many years that refers to a diamond without a distinctive body color. It has been used inappropriately to describe yellow tinted stones. An American Gem Society ruling prohibits the use of this term by its members. Legally a Blue-White diamond must have a blue body color. The many flagrant misuses of this term have rendered it almost meaningless.

BRILLIANCY - Total amount of white light returned to the eye from the gem material 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 popular gemstones, that consists of a round shaped stone with 57 or 58 facets.

BUBBLE - Any transparent inclusion in a diamond. It can also refer to another diamond crystal within a diamond or a grain of a different material.

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

CAMEO - A gem material, usually composed of two or more different colored layers. The top portion is carved in relief above the girdle plane and the bottom portion acts as the background for the carving in addition to giving a depth dimension to the piece. Usually carved in onyx or the traditional material from Italy which is shell.

CANARY - A term referring to the intense hue of yellow in a diamond. Also called "fancy" 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 - Any black appearing inclusions in a diamond caused by the addition of the minerals graphite or hornblende.

CHANGE 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.

CHATOYANCY - The phenomenon of a sharp, well defined band or streak of light across the dome of a gem material caused by the reflection of light from parallel needle-like inclusions.

CHIP - A term that has many uses in gemology, it can refer to a small rose-cut or single cut melee. A cleavage piece of diamond that weighs less than 1 carat, or a curved break in a diamond.

CLEAN - A trade term, usually meaning "free from noticeable flaws."

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 broken with a swift blow. This swift blow splits the stone into proportions for fashioning more economically or for allowing better quality selection.

COLOR BANDING - Uneven color distribution in a gem material; it appears as bands of varying colors or different tones or values of the same color. The bands may be straight, curved or angular in appearance.

COLOR ZONING - Uneven color distribution in a gem material appearing as irregular patches of varying colors or different tones of the same color.

COLORED STONE - A gemstone of any species other than diamond. This usage arbitrarily classifies all varieties, but still does not include colored diamonds. This system has, however, proven to be a practicable and satisfactory general classification.

CROWN - The part of any faceted gemstone above the girdle.

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

CULTURED - A pearl produced by artificially inducing the formation of a pearl sac, usually by the introduction of a shell bead or square mantle tissue into the body of a possible pearl bearing mollusk (oyster or clam).

CUT - Style or form (shape) in which a gem material has been fashioned and/or the proportional dimensions used.

DIAMOND - A mineral that is composed of carbon with a hardness of 10 and that is single refractive. In its transparent form it is the most highly valued of gemstones. The stones can come in all colors of the rainbow and are called "fancies".

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

DOUBLET - An assembled stone of two portions bound together by a cement or fused together by heat. An opal doublet, for example, may be opal cemented to black onyx with a black colored cement.

DURABILITY - A combination of hardness, toughness and stability that describes a specific gemstone's durability.

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 - One of the small, cut and polished planes that is placed on a gemstone to increase brilliancy and beauty. It can also occur naturally as approximately placed planes in the top of a gemstone crystal. This is normal crystal growth.

FACETED GIRDLE - A girdle of a stone that is lapped and polished for maximum surface reflection and has many flat planes around the circumference of the stone.

FASHIONING - Any operation employed in preparing rough gem material into polished gemstones such as cleaving, cutting, or faceting.

FEATHER - A trade term commonly applied to almost any flaw inside a stone and, more specifically, to a jagged irregularly shaped fracture which is white in appearance. In gemology, feather is a term used to describe a series of inclusions which -- under a microscope -- appear as elongated, irregular in shape and grouped together in an orderly proximity that resemble the pattern of a feather on a bird's wing.

FINISH - The term referring to certain details of fashioning such as the placing and polishing of the girdle, culet and facets.

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

FLAW - Any external or internal imperfection of a diamond or other transparent gemstone such as an inclusion.

FLUORESCENCE - The process of a material emitting electromagnetic radiation when it is subjected to radiation. In gemology, the usual influencing radiation is ultraviolet light and the emitting radiation is visible hued light. For example, diamonds under ultraviolet light will often emit a visible light of a blue hue (or other colors).

FOILBACK - Any gem material that has an applied metallic backing to improve color, brilliance and/or phenomena such as a glass, rhinestone-accent stone, or other material.

FOUR C'S - A phrase used to describe a diamond's characteristics, all starting with the letter "C". The four categories used to define a diamond's worth are: cut, clarity, color and carat weight.

FRACTURE - A break or chip in any direction not parallel to the planes of the atoms in a crystalline mineral and other than on or across cleavage planes. In other words, any uneven break.

FRESHWATER PEARL - A pearl that is harvested in a fresh water living mollusk.

FULL CUT DIAMOND - A description of a brilliant cut, round stone. A diamond with 57-58 facets.

GEM - A cut and polished material which possesses the beauty, durability and rarity necessary for use in jewelry. Also used to describe an especially fine specimen such as a gem emerald.

GEMOLOGY - The study of gemstones. It includes the study of their identification, grading and appraisal as well as the examination of their symbols, fashioning, history and marketing.

GIA - (Gemological Institute of America) A nonprofit, endowed, educational institute maintained for the benefit of industry and the public. Many educational courses are offered for advancement and knowledge within and about the trade.

GIRDLE - The outer edge, or periphery, of a fashioned stone; the portion that is usually grasped by the setting or mounting via prongs or bezels. It is the dividing line between crown (top) and pavilion (bottom) of a gemstone. It can be ground, bearded, polished or faceted. It can be cut thick or thin, but is designed to help avoid breakage.

GLASS - An inorganic, amorphous substance that is in a unique physical state. It cools to a rigid state, however, without crystallization. A variety of constituents may be used to create it. The jeweler usually encounters glasses that are mixtures of silica fused with a variety of other substances that impart various desirable qualities such as a low melting point, brilliancy and opacity. Glass is available in many, if not all, colors of the rainbow.

HARDNESS - A gem's ability to resist scratching.

HUE - Any sensation of color other than black, white or gray (a specific color).

IMPERFECTION - A general term used to refer to any inclusion, internal or external in a gemstone -- a feather, carbon spot, knot, fissure, or scratch.

INCLUSION - In its broadest sense, any optically detectable irregularity in a gem material. In a narrower sense, any foreign material caught up during the growing or formation process. Inclusions are usually used to map and identify a specific stone.

INTAGLIO - A gem in which the design has been engraved or carved into the stone.

INTENSITY - The attribute of a color, which determines its position on a scale from vivid to dull. Traces of brown or gray decrease the intensity of a stone (the amount of color saturation).

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.

KNOT - An inclusion that is encountered at the surface of a stone during the cutting and polishing of a diamond. It can stand out as a small raised surface on the finished stone.

LOUPE-VISIBLE - Visible with the aid of a loupe (a magnifying eye piece used to examine a gemstone, usually 10X).

LUSTER - The appearance of a surface in reflected light.

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

MARQUISE - A gem shape that is elliptical but with pointed ends, similar to the shape of the boat.

MELEE - A term used primarily to describe small, round faceted diamonds of approximately .18 carat or less. It is also applied to colored stones in similar sizes as well.

MINERAL - An inorganic substance with a characteristic chemical composition and a definite crystal structure.

MOHS SCALE - A loose scale of hardness, used for field collecting, which allows for identification of specimens. The comparative scale of hardness is as follows: 1) talc, 2) gypsum, 3) calcite, 4) fluorite, 5) apatite, 6) orthoclase, 7) quartz, 8) topaz and beryl, 9) corundum and 10) diamond.

MOUNTING - Trade term for that portion of a piece of jewelry in which a gem or other object is to be set or has been set.

NACRE - The iridescent substance containing aragonite and calcite crystals. This is an important outside layering material and a constituent of a pearl and cultured pearls. The thicker the nacre the longer the pearl has been allowed to grow. This results in longer durability.

NATURAL - A trade term for a portion of the original surface of a rough diamond, usually at the girdle, left by the cutter of a fashioned stone.

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

NAVETTE - Usually considered the same shape as that of a marquise, which is a cut shape where the girdle is similar to the outline of a boat.

NICK - A minor chip out of the surface of a diamond, usually caused by a light blow, found near or on the girdle of the stone (a percussion mark).

OPALESCENCE - Milky or pearly appearance of some common opal, opalescent glass, and other similar substances.

OPAQUE - Transmitting no apparent light; not transparent.

ORIENT - Minute prismatic sheen on or just below the surface of a pearl or cultured pearl caused by the interference and diffraction of light from the minute crystals comprising the nacre.

OVAL CUT - A brilliant style of cutting in which the girdle shape is oval or elliptical.

PAVE - A style of setting small stones as close together as possible in two or more rows.

PAVILION - That portion of a faceted diamond or other gem material that lies below the girdle.

PEAR SHAPED CUT - A variation of the brilliant cut with the girdle outline of the stone; pear shaped.

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.

PIT - An indentation on the surface of a diamond, caused by a blow, knot or the opening of a cavity during cutting or polishing.

PLAY OF COLOR - Variety of prismatic colors seen in rapid succession. A phenomenon seen in opal, fire agate, and other similar stones caused by the interference and diffraction of light.

POINT - A measurement in the weight of a diamond equal to 1/100 of a carat. Thus, .50 carats is equal to 50 points.

POLISH - The smoothness of a surface plane or planes in which optical reflection is maximized and shows no visible wheel or burn marks.

POLISHED GIRDLE - A girdle that has been lapped to yield a uniform highly reflective surface or many surface planes (as in a faceted girdle).

REFLECTION - Returning of light which strikes the surface of a stone.

REFRACTION - The change in the velocities and angles of light rays as they pass obliquely from one medium to another of a different density.

RHINESTONE - Historically, rock crystal quartz in the jewelry trade of the USA. The most common usage is for foilback imitations of diamonds and other gemstones.

ROUGH - Any uncut or unpolished gem material.

SCINTILLATION - The display of reflections from a stone as the stone, the light source and/or the observer moves.

SHEEN - The effect of a mineral's body texture on its surface appearance.

SIMULATED STONES - Any substance fashioned to imitate the appearance of a gemstone.

SINGLE CUT - A brilliant cut (round) with eighteen facets: 8 bezel, 8 pavilion, a table and a culet facet.

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

STABILITY - The ability of a gemstone to resist loss of color, dissolution by chemicals and other forms of deterioration.

STAR FACETS - The eight triangular facets that bound the table of a round, brilliant cut diamond.

SUBSTITUTE - In gemology, any substance represented to be or used to imitate a more valuable gemstone.

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

TABLE - The horizontal, top flat facet on the crown of a faceted gemstone.

TARNISH - Tarnish is the various degrees of surface discoloration of minerals or metals. Tarnishing is a mild, natural form of oxidation that is caused by a chemical variation of the surface molecules due to dust, dirt and/or exposure to air, especially air that contains traces of sulphurous fumes.

TEMPLET - A former name for the kite shaped facets that are cut and polished on the top crown of brilliant cut gemstones.

TESTING STONE AND NEEDLES - A set of tools used to test the gold content of a particular item. A black stone is streaked with the item and several gold tip needles of various karat values. Acid is poured onto the stone and the gold tip needle streak that dissolves at the same rate as the jewelry item's streak is the correct karat gold of the item.

TETRAGONAL CRYSTAL SYSTEM - Crystal growth formed by three axes created at right angles to each other. A gemstone with this type of crystal formation is zircon.

THICKNESS - The metric measurement of a brilliant cut gemstone that is measured from the stone's top table to its bottom culet.

THUMB RING - Thumb rings were first used in the orient (China) during the K'ang Hsi period (1662-1772). They were made of jade, bone, ivory or glass and used by archers to protect their thumbs as they pulled the string of the bow back into the hold position to release the arrow. Over time, the rings slowly became fashionable as a body adornment.

TIFFANY SETTING - Invented by Charles L. Tiffany in 1886, it is the style of setting a single diamond (solitaire) into a ring using a flared prong to secure the stone. The setting usually consists of 4, 6 or 8 prongs that bend slightly over the girdle of the gemstone to keep it secure.

TINTING - A technique of enhancing or neutralizing a gemstone's color. Enhancing a gemstone involves painting the pavilion facets of the stone to improve its color. Neutralization is used to tone down the yellow of a diamond. This is done by painting violet dye around the girdle of a diamond (or also the pavilion facets). It has been used since the 16th century, even prior to the origin of the brilliant cut. Tinted gemstones are usually set in a closed setting to hide the fact that the stones have been altered.

TONE - An attribute of color which determines its lightness or darkness of shading.

TORCH - A tool that disperses heat by using various gases mixed with oxygen. The cleanest torches use natural gas, propane, and hydrogen.

TOUGHNESS - The opposite of brittleness. It is the ability of a mineral, element, crystal or gemstone to resist breakage (fracturing) when struck. Toughness is not the same as the hardness of a stone.

TRANSITION ELEMENTS - Types of metals that because of their atomic structures allow absorption and refraction of light in a variety of degrees. Such elements are titanium, chromium, copper, cobalt, iron, manganese, vanadium and nickel.

TRANSLUCENT - Passing light imperfectly through a gemstone; blurry or cloudy.

TRANSPARENCY - The ability of a substance to transmit light. In gem testing terms transparency is called " diaphaneity." The degrees of transparency are:

  1. Transparent (glasslike) - The object clearly transmits light. Transparent substances include quartz, diamonds, and glass.

  2. Translucent - There is no clear vision through the gemstone. Examples include jade and green onyx.

  3. Opaque - No light is able to pass through the substance.

TREATED DIAMOND - A diamond that has been irradiated, neutron-treated, cyclontroned, electroned, exposed to radiation (radium bromide), or given any other modern treatment. In some cases, these processes are used to color the diamond so that it will appear as a shade of blue, green, red, yellow, orange, brown, black or pink. Other processes are used to bleach the stone of any color. The first experiments using these processes took place in 1904 and were done by Sir William Crookes. His first colored diamonds were done by radiation and his green stones are still radioactive to this day. Lab tests can distinguish if a diamond has been treated.

TRI-COLORED GEMS - Specific gems that have three distinct colors because they formed near various minerals which colored a specific area of the original crystal. An example of a tri-colored gem is a "watermelon tourmaline."

TRIGONAL OR (RHOMBOHEDRAL CRYSTAL SYSTEM) - One of three-fold symmetry crystal growth or uniaxial. Many gemstones commonly used in jewelry have this type of crystal system. Examples include as tourmaline, quartz, calcite and corundum.

TRILLION - A deltoid 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.

TRILOBITE - A fossil marine animal of many varieties and sizes that is used for jewelry and by collectors as a unique example of early geological periods. You can see many examples of these unusual creatures at Ralph Miller Jewelers.

TRIPLET - A technique of combining various or similar gemstones in three layers to create an imitation gemstone. For example, an opal triplet is a thin layer of opal sandwiched between a quartz top and a colored matrix backing material such as black onyx. It is held together by gem cement or gelatin to enhance the color. Please note that extreme care must be taken in cleaning any jewelry that has a triplet or doublet (two layers of material) mounting. Do not soak them in any jewelry cleaner or use an ultrasonic cleaner. Please see our proper care and cleaning section on this web site.

TRIPOLI - A polishing abrasive for metals often used as a preliminary cleaning tool to remove filing marks before the final cleaning of the item using rouge polish.

TROY OUNCE - A weight unit for precious metals predominately used in England and the United States. Twenty pennyweights (dwt) equals one troy ounce and twelve troy ounces equals one troy pound.

TUMBLING - A technique of polishing ordinary quality gemstones. The stones (hopefully all of the same hardness) are placed within a barrel. This barrel is then revolved and spun to combine the stones with water, grit or polishing powders. It was used in the 1600's prior to the technique of faceting.

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

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 to also add heat to the cleaning procedure. When using this type of cleaner extreme care is recommended because certain gems can not withstand the heat and vibration. (Please consult this web site's cleaning recommendations for each specific stone).

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

UNIAXIAL - Minerals (crystals) that have the unique property of single direction refraction or one optic axis. Because of this cutters must align rough pieces for proper visibility of the light reflection when preparing the gemstone. The stone's brilliance can be lost if axis alignment is not carefully controlled.

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

VITREOUS ENAMEL - A fine ground power of various colored glass that when heated in the correct procedures will permanently adhere to metals to create decorative colors and patterns.

WEIGHTS - The metric measure for gemstones and jewelry that uses the carat as its base. The carat is further broken down into points and grains. It was first used in 1913.

WET GRIND - A technique of grinding stones using water as a lubricant. Historically, a mixture of water, clay, salts and enamel frit (small pieces of glass) was used. Using this mixture, decoration was added to the piece by dipping or spraying it onto the object before it was fired.

WHITE GOLD - An alloy of yellow gold which has silver, zinc, or platinum as a whiting agent.

WHITE OPAL - A type of opal, usually associated with precious white opal found in Australia, that contains a variety of colors and flash plates.

X-RAYS - Electro-magnetic radiation. Used by man as a treatment for some stones to enhance their beauty.

YELLOW GOLD - A specific color of gold when its in its natural state.

ZIRCON CUT - A type of a brilliant cut that adds an extra 16 small facets at the bottom of the pavilion cuts (near the culet) that can increase a stones brilliance.