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