Here is a few of the terms that jewellers and gemmologists use, and their meanings:

  • A jour: a type of setting which allows light to enter the pavilion of a faceted stone
  • Adularescence: The appearance of a floaty, billowy light in cabochon gemstones, or a stationary sheen on the flat surface of a stone
  • Ajouré: Pierced or openwork in metal
  • Amethystine: The colour violet to purple in gemstones
  • Angle of refraction: The angle at which a reflected ray of light leaves a surface as measured from the normal
  • Anisotropic: The gemological term for double refraction
  • Annealing: Toughening and softening a metal by heating
  • Artificial stone: A man made imitation or synthetic gem
  • Assembled stone: A gem constructed of two or more ports
  • Asterism: The appearance of a rayed figure or a star in a gemstone, caused from the reflection of light from minute inclusions
  • Aventurescence: A glittery appearance on the surface of a gemstone
  • Birefrengence: The numerical measurement of double refraction
  • Black onyx: A common misnomer for black chalcedony
  • Body colour: The dominant hue in a gemstone
  • Brilliancy: The total amount of white light returned to the viewer of a gemstone
  • Bruting: A method of shaping a rough diamond, by rubbing one diamond against another
  • Cabochon: A gemstone with an unfaceted dome shape
  • Calibré cut: Small gem material used for pavé settings, or small stones cut to a particular shape and size
  • Cameo: A gem or shell material with two distinct colour layers, carved in relief with the lower layer as a contrasting background
  • Carat: A measurement of weight, equal to one fifth of a gram
  • Chatoyancy: The appearance of streaks of light across the surface of a gemstone; may appear as a single band of series of bands
  • Cleavage: A smooth break or separation of a gemstone along the direction of it’s crystal structure
  • Cloud: A small group of white inclusions in a diamond
  • Colour Zoning: Uneven colour in a gemstone
  • Coloured stones: A gemstone other than a diamond
  • Critical angle: The greatest angle measured from normal at which light can be refracted out from a stone
  • Crown: The part of a faceted gem above the girdle
  • Crystal system: The classification of minerals according to the geometric form of their crystals
  • Culet: A small polished surface, at the point of ridge of a gemstone, used to reduce chipping
  • Dichroism: The transmission of two different colours from a gemstone (best viewed with a dichroscope)
  • Dispersion: The separation of light into its spectral colours as it passes through a gemstone
  • Double refraction: The separation of light into two separate beams in a gemstone.
  • Doublet: An assembled stone of two parts
  • Durability: A combination of hardness, toughness and stability
  • Facet: A planear surface polished on a gemstone
  • Fancy diamond: A diamond with a strong body colour
  • Feather: An inclusion within a gem, often with a white irregular look
  • Fingerprint inclusion: Liquid or gas inclusions on a gemstone, aligned in the form of a human fingerprint
  • Fire: The play of colour on or within a gemstone as a result of dispersion
  • Flaw: A visible inclusion in a gemstone
  • Fluorescence: The emission of visible light when a gemstone is exposed to ultraviolet light
  • Foilbacked: The addition of a metallic foil to the pavilion of a gemstone to improve its face-up colour
  • Fracture: A break or chip in a gemstone along anything other than a cleavage plane
  • Girdle: The outer edge of a gemstone
  • Grisaille: An enameling technique of built-up layers of black and white enamel
  • Hardness: A gemstone’s ability to resist scratching
  • Heat treatment: Altering or improving a gem’s appearance by heating
  • Incandescence: The emission of light caused by heating
  • Inclusion: A visible irregularity in a gemstone
  • Intaglio: A design carved on the surface of a gemstone (the opposite of a cameo)
  • Iridescence: Spectral colours observed on a gemstone (Similar to the sheen on the surface of bubbles)
  • Matrix: The rock in which a gem is found
  • Millegrain: A style of setting in which there is a tiny rows of beads along the edge of the setting
  • Natural pearl: A pearl which occurs without the aid of man
  • Normal: In the study of light, an imaginary line perpendicular to a surface
  • Opalescence: Milky or pearly appearance
  • Optic character: The effect a gemstone has on the transmission of light
  • Overtone: A tint of colour on the body of a pearl
  • Parting: Flat, smooth breakage of a mineral along planes os twinning
  • Pavilion: The portion of a faceted gemstone below the girdle
  • Phenomenon: An optical effect in gemstones, often enhanced by proper cutting
  • Phosphorescence: A continuing glow emitted after the light source has been removed
  • Play of colour: Prismatic flashed of colour seen in a gemstone
  • Refraction: The change of velocity of light and subsequent bending of it
  • Refractive index: The ratio of the speed of light in air to the speed of light within a substance
  • Refractometer: A device to measure the refractive index of a gemstone
  • Rough: An uncut of unfashioned gemstone
  • Scintillation: Reflections from a polished surface as its position relative to the viewer or the source of illumination changes
  • Stability: The resistance of a gemstone to deterioration
  • Table: The flat horisontal surface on the crown of a faceted gemstone
  • Toughness: Resistance to chipping or breaking
  • Trichroism: The transmission of three different colours in three optical planes as light passes through a gemstone

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