Gemological Terms, Tools, & Properties

4 C's

4 C’s

Diamonds, by nature of their unique characteristics, can be evaluated much more precisely than other gems. Their extreme hardness allows ...
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6.79 Carat French-Cut Diamond, Angeled View.

Adamantine Luster

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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Raymond Yard Moonstone Brooch and Earrings.

Adularescence

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

Aggregate

Aggregate in the geologic or gemologic sense of the word, is defined as a composition of various materials (usually mineralogical ...
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Synthetic Alexandrite-Like Sapphire and Enamel Art Deco Ring.

Alexandrite-Like

 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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Edwardian_Sapphire_Diamond_Ring

Allochromatic

 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 Fan

Alluvial

Alluvial means 'deposited by water'. The word 'alluvial' is derived from the Latin word 'alluvius', from 'alluere', which means 'to ...
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Amorphous vs Crystalline structure

Amorphous

An amorphous substance is one that has no regular arrangement of atoms; it literally means "without form". Examples of materials ...
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Star Ruby, Diamond, Platinum Ring Exhibiting Asterism.

Asterism

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 in Goldstone.

Aventurescence

Aventurescence is a phenomenon in gemstones whereby glittering reflections of small inclusions of hematite or goethite in feldspar or fuchsite ...
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Doubling Zircon

Birefringence

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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Bodycolor,cream

Body Color

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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Boule

Boule

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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6.79 Carat French-Cut Diamond, Angeled View.

Brilliance

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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Conch Pearl Ring.

Calcareous Concretion

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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Carat

Carat

A unit of weight for gemstone materials. One carat equals 0.200 grams ...
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Cat's Eye Chrysoberyl and Diamond Ring.

Cat’s-Eye

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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Color Change Sapphire.

Change of Color

 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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Cat's Eye Chrysoberyl, Diamond, Platinum Ring Exhibiting Chatoyancy.

Chatoyancy

An optical phenomenon which appears as a bright band of light across certain gemstones that when cut as cabochons, reproduce ...
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Emerald and Diamond Ring with Typical Emerald Inclusions.

Clarity

A very included spessartite garnet. This stone has a very low clarity grade of I3. The grading of a gemstone ...
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The Cleaving Directions in an Octahedral (left) and Dodecahedral (right) Diamond Crystal.

Cleavage

DefinitionThe ability of a material to split along a certain plane or planes with weak atomic bonding. A crystal structure ...
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Multi-Gemstone Necklace.

Colored Stone

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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Opal Doublet/Triplet

Composite Stone

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

Crown-Gemstone

Crown, Girdle, Pavilion.The crown of a gemstone refers to the part above the girdle ...
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Early 20th Century Pin Centered with a Translucent Oval Cabochon Chrysoprase Chalcedony. Image Courtesy of Lang Antiques

Cryptocrystalline

Having crystals so small that individual crystals cannot be seen under ordinary optical microscope, but are detectable by effect under ...
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Quartz Crystal with Vitreous Luster.

Crystalline

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

Culet

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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Transparent Rock Crystal Quartz Bead Necklace.

Diaphaneity

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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Dichroism

Dichroism

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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Dichroscope

Dichroscope

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

Diffusion

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 Hunt.

Dispersion

Synthetic Rutile Showing a High Amount of Dispersion. Image Courtesy of Jeffrey HuntThe separation of white light into the component ...
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Zircon has a Very High Birefringence which is Clearly Visible in this Shot. The Back Facets Appear Doubled. Image courtesy of Jeffrey Hunt.

Double Refraction

The property of splitting a single beam of light into two polarized beams which pass through a crystal at different ...
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Doublet

Doublet

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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Art Nouveau Ivory and Gold Mermaid Brooch.

Dull Luster

Dull luster describes the luster of Ivory. Japanese Shibayama Ivory Box with Dull Luster ...
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Durability

Durability

Durability refers to a quality of gemstones to withstand wear and tear in normal use. It depends on hardness (the ...
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Natural Amethyst and Heat Treated Amethyst-Gone-Citrine

Enhancement

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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Coco Chanel Faux Pearl, Turquoise and Rhinestone Necklace.

Faux

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 Hunt.

Fire

Synthetic Rutile Showing a High Amount of Dispersion. Image Courtesy of Jeffrey HuntA popular term used to describe the flashes ...
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Fluorescence

Fluorescence

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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Conchoidal

Fracture

A break or chip, caused by stress, that is in any direction other than parallel to the planes of atoms ...
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Vintage Black Opal and Diamond Ring Exhibiting Play-of-Color.

Gem Phenomena

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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Multi-Gemstone Necklace.

Gemstone

A gemstone is a stone of organic or inorganic - such as mineral - nature. The difference between a mineral ...
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Arts & Crafts Moonstone Bracelet Exhibiting Girasol.

Girasol

Any gem variety that exhibits a floating, milky sheen that moves about as the stone is turned or as the ...
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Art Deco Gota De Aceita Emerald Brooch.

Gota de Aceita

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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Serpentine Paten with Gold Inlay Surrounded by Gems in Gold 1st Century BC. In the Collection of the Louvre, Paris.

Greasy Luster

Greasy is the term used for the surface reflection on materials as seen on Serpentine. Serpentine Paten with Gold Inlay ...
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Moh's Scale of Hardness. Photo Courtesy of the National Park Service.

Hardness

Hardness in jewelry terms (and gemology) means the ability of a subject to withstand abrasion by another subject. The most ...
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Hardstone Cameo Depicting Athena Wearing a Helmet with a Live Serpent on Top and a Secondary Visage on the Visor. Her Chest Armor Displays the Aegis of Zeus.

Hardstone

Hardstone Cameo Brooch made in Sweden. Hardstone is a term used loosely to refer to any hard gem material used ...
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