Gemological Terms, Tools, & Properties

Adamantine is the term used to describe the luster exhibited by diamonds and gems with a Refractive Index of 1.9 - 2.5. The root word adamant ...
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Adularescence is an optical phenomena often called the “moonstone” effect. The phenomenon is applied to feldspar, usually orthoclase that, when ...
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Aggregate in the geologic or gemologic sense of the word, is defined as a composition of various materials (usually mineralogical ...
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 Alexandrite-like refers to the ability of a gem material to change colors when viewed under different light sources such as daylight and ...
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 The term allochromatic is used in reference to gem materials that derive their color from elements that are not an ...
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Alluvial means 'deposited by water'. The word 'alluvial' is derived from the Latin word 'alluvius', from 'alluere', which means 'to ...
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An amorphous substance is one that has no regular arrangement of atoms; it literally means "without form". Examples of materials ...
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Asterism is an optical phenomenon that results in the reflection of light rays on a gemstone, cut en cabochon, forming a ...
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Aventurescence is a phenomenon in gemstones whereby glittering reflections of small inclusions of hematite or goethite in feldspar or fuchsite ...
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Birefringence is the strength of double refraction as measured by computing the difference between the high and low indices of a ...
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Body color refers to a pearl's overall color. White, cream, pink and black are the most commonly seen body colors. The ...
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Split Boules of Flame Fusion Corundum.Photo by Morion Company.Boule refers to the rough form of synthetic corundum or spinel, produced through the flame fusion/Verneuil ...
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Brilliance is a term used to quantify the brightness of a gemstone. Brightness, and therefore brilliance, are related to the surface ...
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Calcareous concretions are pearl-like growths produced in mollusks that lack nacre. While still composed of calcite and aragonite, the crystals are much coarser. Some ...
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A unit of weight for gemstone materials. One carat equals 0.200 grams ...
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Cat's-Eye is an optical phenomenon (also known as chatoyancy) whereby light reflects back off a gemstone, cut en cabochon, as a single ...
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 A phenomenon of some colored gemstones in which the gem material appears a different color in incandescent light than in daylight ...
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An optical phenomenon which appears as a bright band of light across certain gemstones that when cut as cabochons, reproduce ...
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A very included spessartite garnet. This stone has a very low clarity grade of I3. The grading of a gemstone ...
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DefinitionThe ability of a material to split along a certain plane or planes with weak atomic bonding. A crystal structure ...
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Colored stones are all gemstones that are not a diamond. The term is used as a general catch-all for gemstones.Georgian Style ...
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Composite Stone - Triplet. Composite stones are gem simulants that are composed out of several materials. Doublets and triplets are good examples. Composite stones ...
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Crown, Girdle, Pavilion.The crown of a gemstone refers to the part above the girdle ...
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Having crystals so small that individual crystals cannot be seen under ordinary optical microscope, but are detectable by effect under ...
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A crystalline material is a substance with a regular, repeating, 3-dimensional atomic structure. We divide crystalline materials into monocrystalline and ...
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Culet. The tip of the pavilion is called the culet. Sometimes in the form of a facet, sometimes as a sharp point ...
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Diaphaneity is the general term to describe the transmittance of light through an object. The three typical classifications are transparency, translucency, and opacity ...
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The property of many doubly refractive colored gemstones of transmitting two different colors in two different vibration planes due to differences of selection absorption ...
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A small gemological instrument that is used to detect pleochroism in a material. Using either a calcite crystal or polarizing ...
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Diffusion treatment is a treatment used to alter the color of a gemstone (mostly sapphires). Smaller atoms, usually beryllium, enter ...
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Synthetic Rutile Showing a High Amount of Dispersion. Image Courtesy of Jeffrey HuntThe separation of white light into the component ...
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The property of splitting a single beam of light into two polarized beams which pass through a crystal at different ...
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A composite gemstone consisting of two pieces of the same or different gem materials, or one gem material and a second of ...
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Dull luster describes the luster of Ivory. Japanese Shibayama Ivory Box with Dull Luster ...
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Durability refers to a quality of gemstones to withstand wear and tear in normal use. It depends on hardness (the ...
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Laser Drilled Diamond. The Visible Drill Channels are Not All Individual Channels, for the Most Part, They are Reflections.Image Courtesy ...
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Faux (from French: "false") is the name given to imitation jewelry, in particular to simulated pearls.Coco Chanel Faux Pearl, Turquoise and Rhinestone ...
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Synthetic Rutile Showing a High Amount of Dispersion. Image Courtesy of Jeffrey HuntA popular term used to describe the flashes ...
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The emission of visible light by a material, such as a diamond, when illuminated by ultra-violet light or X-radiation. A ...
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Diamonds, by nature of their unique characteristics, can be evaluated much more precisely than other gems. Their extreme hardness allows ...
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A break or chip, caused by stress, that is in any direction other than parallel to the planes of atoms ...
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Gem phenomena, or optical phenomena, are the observable characteristics of gemstones, such as asterism, play-of-color and chatoyancy. Phenomena are usually a result of light interacting ...
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A gemologist is someone who is certified by a specialty school, college or university in the identification and evaluation of ...
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A gemstone is a stone of organic or inorganic - such as mineral - nature. The difference between a mineral ...
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GIA is the abbreviation for the Gemological Institute of America. It was established in 1931 by Robert M. Shipley (a ...
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Any gem variety that exhibits a floating, milky sheen that moves about as the stone is turned or as the ...
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In addition to the streamlined geometric styling, fine Art Deco jewels of the 1920s-30s are noted for their superior gemstones and here we have ...
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Greasy is the term used for the surface reflection on materials as seen on Serpentine. Serpentine Paten with Gold Inlay ...
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