Adularescence
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White or silver-blue haze displayed by high quality moonstones and other gems.
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Alluvial Deposits
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Gem deposits found in water after they have been separated from the mother rock.
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Appraisal
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An evaluation performed by a licensed gemologist to determine the replacement value of a gem or piece of jewelry.
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Asterism
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A star effect displayed by certain gems with intersecting inclusions.
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Baroque
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Oddly shaped pearls that form during cultivation.
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Brilliant cut
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A round shaped stone that has a minimum of fifty-eight facets.
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Cabachon cut
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The rounding of a gem without facets into the shape of a highly polished dome.
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Cameo
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The art of carving a shell or similar material above its background.
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Carat
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A unit of weight for gems.
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Chatoyancy
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The ability of certain gems to display a "cat's eye" effect, caused by the precise occurrence of narrow
inclusions.
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Cleavage
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The breakpoint or weakness of a gem, connected to its atomic structure. Gems with perfect cleavage are most
likely to break when being cut or faceted.
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Color
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An important property used in the evaluation of a gem. The quality of a gem can be measured based on either
the presence or the absence of color.
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Conchiolin
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Dark substance secreted by a mollusk during cultivation.
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Crown
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The top part of a gemstone.
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Culet
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The lowest part of a gemstone.
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Cultivation
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The process used to form a pearl by inserting tissue from a donor mollusk into another.
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Dichroism
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The ability of some gems to display a second color when viewed from a different angle.
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Dispersion
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The splitting of light as it enters a gemstone. Also called the stone's "fire".
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Doublet
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A stone made of two components, generally held together with a clear adhesive.
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Facet
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The cut and polished part of a gemstone.
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Fire
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The rainbow or colors that come from light rays as they enter a gemstone.
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Fluorescence
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The ability of some gems to glow when heated in low light.
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Foiling
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The practice of placing a colored or silver foil behind a gem in a closed setting to enhance its appearance.
This is often done with rhinestones.
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Full Cut
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A round-shaped, brilliant-cut gemstone.
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Gemstone
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A mineral or combination of minerals that display a high degree of beauty, rarity, durability and desireability.
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Geode
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A hollow rock cavity usually containing some form of one or more gemstones. Amethyst and Peridot are examples
of gemstones found in geodes.
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Girdle
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The widest point in circumference of a gem.
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Gram
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A unit of measurement of weight used to express the weight of a gem. Just over 28 grams equals one ounce. One
thousand milligrams equal one gram.
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Heat Treatment
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The application of heat to a gemstone for the purpose of improving its color.
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Illusion Setting
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Any setting that is not as it appears. This is often done by combining several small diamonds with rhodium to
give the impression of a higher carat weight.
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Inclusions
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Foreign matter that occurs within a stone and displays a different color or effects from the rest of the stone.
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Iridescence
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The play of color in a gemstone resulting from inclusions.
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Karat
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Unit of measurement that indicates the quantity of fine gold in a piece of jewelry. This is always based on
pure 24-karat gold, eg. 18 karate gold contains eighteen parts fine gold and six parts metal alloys.
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Lapidary
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A skilled craftsman who cuts and polishes gems to their finished state.
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Luster
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The outward appearance of a gem or organic material. Luster is important especially when evaluating the quality
of pearl.
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Mineral
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An inorganic element of the Earth of consistent atomic structure and chemical composition.
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Moh's Hardness Scale
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Numerical scale developed by Friedrich Mohs that assigns a rating to a gem according to its ability to resist
scratching, the hardest being 10 and the softest being 1.
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Opalescence
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A variety of iridescence that is most often light blue in color.
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Organic Gem
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Matter that is not technically a gemstone, but is derived from animal or plant life. Organic gems include amber,
coral, ivory, jet, pearl and tortoiseshell.
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Oxidation
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The breakdown of a metal over time as a result of exposure to oxygen and other natural elements.
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Pave (Pah-vay)
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A jewelry setting whereby one prong is touching three or more stones. If not, it is classified as a cluster.
The pave setting is popular with diamonds.
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Pavilion
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The lower portion of a gemstone that begins just below the girdle.
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Pearl Essence
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A liquid coating that adds a pearl like luster to simulated pearls. It is derived from the scales of a herring.
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Pleochroism
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The ability of certain gems to display two or more colors when viewed from different angles.
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Points
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Units of measurement to express the carat weight of a gem. One carat is equal to one hundred points.
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Precious gem
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A term that was once reserved only for the diamond, emerald, ruby and sapphire. Today, the quality of a given
gem can place it in the precious category.
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Precious metals
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Defined by the industry as gold, silver, platinum and palladium. Unlike gemstones, the term precious is
still widely accepted to delineate metals.
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Primary Deposit
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When a gem or mineral is found resident in its original rock.
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Refraction
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The bending of light as it enters a gemstone and slows down.
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Refractive Index
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A process developed by Willebrord Snell that incorporates a refractometer to measure the speed and angle of
light as it enters a gemstone. It is used in gem identification.
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Rose Cut
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An age old art of faceting a stone to look like an opening rose.
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Rough
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In gemology, this refers to the raw, natural state in which gems are found.
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Rutiles
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Needle-like inclusions (or foreign matter) within a stone, which can produce some gem phenomena as an asterism
(star) and a cat's eye, depending on the direction of the rutiles.
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Scarab
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A stone carving that shows the sacred scarab beetle in intricate detail. The ancient Egyptians revered the scarab
as a symbol of the soul.
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Secondary Deposit
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A deposit of gems that has been worn away from its original site, usually by the effects of weather. An alluvial
deposit is one example of a secondary deposit.
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Semiprecious gem
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At one time, this term referred to all gems other than diamonds, emeralds, rubies and sapphires.
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Shaving
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Cutting a stone generously across the table, while allowing for very little depth. Shaving makes a stone appear
to have a higher carat weight than it does.
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Sheen
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Another name for iridescence.
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Simulant
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A human-created gem having the same look, but not the same physical properties, as its natural counterpart.
Cubic zirconia has a diamond like appearance, but none of a diamond's properties.
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Single Cut
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Stones consisting of seventeen facets or less.
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Soude
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Assembled gems of multiple layers held in place by an adhesive. Also known as a triplet.
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Species
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A gem with distinctive characteristics that are well defined.
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Specific Gravity
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In gemology this refers to a process that determines the weight (or density) of a gem when compared to that
of an equal volume of water. The result is a ration expressed as a single number.
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Step Cut
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Cutting a gem with rectangular facets along the perimeter.
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Swiss Cut
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Stones consisting of thirty three facets.
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Synthetic gemstone
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A man-made stone that, unlike a simulant, has the same chemical composition and crystal structure as its natural
counterpart.
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Table
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The flat top part of a gemstone.
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Table Facet
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Central facet on the table (or crown) of a gem or simulant.
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Trichroism
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Those gems that display three different colors when viewed from different angles.
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Triplet
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A man-made creation of three parts that normally includes a clear protective top layer fused together with a
thinly sliced gem and a clear or colored adhesive.
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Veins
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In gemology this term is loosely used to describe long thin lines that occur on the surface of the gem. The
black lines seen in turquoise or howlite are an example of veins.
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