Gemstones More Definitions

Gemstones Definitions

Common Terms Used With Gems

• Abrasion - Damage to a facet edge, culet or keel line.
• Adamantine - Quality of luster - like that of a diamond.
• AGS - American Gem Society, Las Vegas, USA
• Baguette - Rectangular narrow gem cut.
• Tapered - Gemstone cut in a trapezoid shape, one end narrower
• Beard - Featherlike inclusion located on the girdle of a diamons and usually a result of improper bruting.
• Bezel - Angled surface on a gemstone's crown - between girdle and table.
• Bow Tie - Term used to describe a dark area seen through across the table of a diamond.
• Briolette - Pear shaped faceted gemstone
• Brilliance/Luster - Intensity of the light reflecting from a gem, observed through the crown.

• Brilliant Cut - Collective name for diamond cuts where lower facets radiate from the center of the gem towards the girdle - round cut is most common.
• Bruise - Crumbled area on a cut gem's surface, caused by a blow.
• Buff Cut/Cab Top - A cut combining the features of a cabachon top with a faceted pavilion. Popular in men's jewelry. Minimizes facet junction abrasion.
• Bruting - A process of shaping the girdle of a rough diamond.
• Burn Mark - Mar on a gemstone facet surface due to overheating during polishing.
• Cabachon - A gemstone fashioned with a domed or convex smooth and polished surface.
• Cape (Color) - A term used to describe yellow diamonds found in the M to Z range of the color grading scale.
• Carat - Standard unit of weight for gemstones - 1 carat = .2 gm
• Cavity/Pit - An opening or indentation on the surface of a gemstone).
• Certificate - Document provided by accredited laboratory defining a gemstones type, weight, color, clarity, proportions, finish grade, treatments. etc.

• Chaton - A generally spherical stone that is faceted.
• Clarity - Relative freedom from inclusions and imperfections of a gemstone. Usually expressed in a fixed grading scale for diamonds.
• Cleavage / Feather - Break or fracture in the stone, internal or external and usually occuring along the crystal's growth planes).
• Cleavage Plane - Plane parrallel to a crystal face.
• Cloud - Milky area in a gemstone; made up of a multitude of very small inclusions.
• Color Diamonds - Range from white to brown of a diamond and usually defined by standard nomenclature. Generally ranges from D - M.
• Color Change - Ability of a gemstone to change hue/color when viewed under different types (wavelengths) of light. e.g. Alexandrite, color change sapphire.
• Colored Gems - The dominant hue of a gem. Identified by position on color wheel or by wavelength.
• Crown - Portion of gem stone above the girdle.
• Crystall incllusion - A crystal in a gemstone. Common in certain species of colored gems

• Culet - Point or small facet at the convergance of pavilion facets.
• Cushion - Square or rectangular cut with rounded corners. Numerous variations.
• Cut - Proportions, make and finish of a polished gemstone.
• D - Best color grade for diamonds. Very white.
• Dead stone - A gemstone so heavily included that no brilliance can be observed.
• Dispersion - Intensity of lightobserved through the crown of a gemstone.
• Emerald Cut - Rectangular or square step cut with diagonal corners.
• External characteristics - Imperfection on a gemstone's surface.
• Facet - Flat polished surface on a finished stone.
• Faceting - Process of creating facets on a gemstone.
• Fancy color - Naturally colored diamonds with varying degrees of rarity.
• Fancy Shape - Any shape other than a brilliant cut.
• Fashioning - Process of manufacturing, i.e. designing, cleaving, sawing, bruting preforming, cutting and polishing.
• Feather - Break or fracture in a stone, internal or external.
• Finish - Quality of a gemstone's polish.

• Fire/Brilliance/Internal Luster - Intensity and quality of light reflecting from a gemstone and observeed through the crown.
• Fisheye - Usually diamonds where pavilion is too shallow. Result is a circular reflection of the girdle that can be seen through the table.
• Fluorescence - Visible light occasionally emitted from diamonds during exposure to ultraviolet light.
• C's - Carat, Cut, color & Clarity; fourof the factors used in determining the value of a gemstone.
• Gem / Gemstone - Mineral or organic material with sufficient beauty, rarity and durability to be set into jewelry.
• GIA - Gemological Institute of America,Carlsbad,USA
• Girdle - Edge located between a gemstone's pavilion and crown.
• Girdling - Process of shaping the rough stone's girdle.
• Grain - Weight unit equivalent to 0.25 carats.
• Graining - Natural iIrregularities seen internally or externally in the crystal structure of a gemstone. Often mistaken for polishing lines.
• Hardness - A gem material's resistance to wear/ scratching measured on Mohs hardness scale.
• Heart Shape - Modified brilliant cut with heart-shaped girdle, usually 56 facets. Cut is often to remove inclusions in an otherwise cleaner gem.
• Hearts & Arrows - A gem cut to ideal proportions &l symmetry. Shows eight hearts shapes in a pavilion view and eight arrowsin a crown view, but only when observed through special viewers.
• HRD - Hoge Raad voor Diamant (Diamond High Council), Antwerp, Belgium
• IDC - International Diamond Council, Amsterdam, The Netherlands
• IGI - International Gemmological Institute, Antwerp, Belgium
• Imperfection - Blemish in a stone which occasionally reaches the exterior.
• Included - One clarity grade which refers to eye-visible inclusions. I1,I2,I3.
• Inclusion - Internal characteristic.
• Industrial diamonds - Non gem quality diamonds.
• Internal characteristics - Imperfection located within the stone.
• Internal reflection - Light reflected off an internal surface of a gemstone.
• Kimberlite - Volcanic diamond-bearing rock (also called blueground).
• Laser Cut - Fashioning a gem's eventual shape using a laser
• Laser Inscription - Laser engraved identifiyng text or numerals, usually on the girdle.
• Laser Sawing - Laser division of a crystal.
• Leveridge Gauge - Tool used to measure dimensions of a mounted or unmounted gemstone.
• Lively stone - A stone with good brilliance and luster.
• Loupe - Small magnifier used to examine gems. Usually 10X.
• Loupe Clean - No inclusions seen under 10X magnification.
• Make - Quality of symmetry and finish of a polished gem.
• Marquise - Symmetrical boat shaped brilliant cut gem with pointed ends.
• Masterstones / color samples - A set of polished gems which have been color graded by an accredited laboratory. Used to color-grade diamonds.
• Mohs - Scale used to determine the hardness of minerals.
• Natural - An original surface on a rough gemstone that is left untouched on the polished stone. Usually found on girdle.
• Nick - Small chip on a gem surface or facet junction usually as result of contact with other stones.
• Oval - Modified brilliant cut with an obround shaped girdle outline.
• Parcel Paper - Folded papers used to hold polished or rough diamonds.
• Pavilion - Part of a gem below the girdle.
• Pavilion facet - Polished surface on the pavilion of a gem.
• Pear Shape/Teardrop - Asymmetrical cut with one pointed and one rounded end.
• Percussion Mark - crumbled area on the surface of a fashioned gem and normally resulting from a blow - usually white.
• Pinpoint inclusion - Very small inclusion of any color indistinguishable as a crystal.
• Pit/Cavity - Small opening on the surface of a polished stone.
• Point - Weight unit, .01 (1/100) carat.
• Pointer - Term used in describing polished stones under 1 carat.
• Polishing lines - Small parallelmarks left on facets during the polishing process.
• Polishing wheel - Flat cast iron wheel upon which gems are polished.
• Princess - Modified brilliant cut with a square or rectangular girdle outline featuring 57 facets.
• Proportions - Relative symmetry of angles and measurements on a polished gem.
• Quality - Term used to descibe the overall color, clarity and cut attributes of a stone.
• Radiant - Rectangular gemstone cut, often 70 facets, combining the shape of an emerald cut and sparkle of a brilliant.
• Reflection - Return of light to the eye after striking an external or internal surface of a facet.
• Rose Cut - Cutting style that produces a flat unfaceted base and a dome-shaped top covered with a variable number of triangular facets and terminates at a point.
• Rough - Gem at found in nature before undergoing any manufacturing process.
• Round Cut - Round brilliant cut.
• Sawing - Process during which a rough gem is cut.
• Scratch - Damage to a polished facet, usually appearing as a faint white irregular line. Often due to contact with other gems.
• SI - Clarity grademeaning slightly included: SI1 and SI2.
• Simulants - Natural or synthetic substances meant to resemble a genuine gemstone.
• Star Facet - Tiangular facet on the crown of a brilliant cut next to the table.
• Symmetry - The accuracy with which a gem is fashioned to a mirror image.
• Synthetic - Non-natural, laboratory produced.
• Table - Large facetat the center of the crown.
• Thermal Conductivity - Ability of a material to conduct heat.
• Trillion - Cut triangular shaped often 44 facets.
• Ultraviolet - (Above Violet) Upper end of the light spectrum and invisible to the human eye. Shows fluorescencein gemstones.
• VS - Gem clarity grade meaning Very Slight; VS1 & VS2.
• VVS - Gem clarity grade meaning VeryVery Slight; VVS1 & VVS2.
• Wavy Girdle - Girdle in a gemstone which has been improperly fashioned and does not run evenly.
• Weight - Gem weight measure - carats, subdivided in grains and points.
• White - A term to describe colorless gems and diamonds D- H colorgrade.
• Yield - Carat weight remainding after polishing - often expressed as a % of rough weight.