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- Abalone also known as ear-shells, produce pearls of various hues, such as greens, yellows, blues.
- Abrasive material hard, and sometimes brittle, substances used for abrading and polishing purposes, eg, diamond dust, boron carbide (B4C), carborundum , aluminium oxide, garnet, emery, etc. Diamond dust, the most important, is made in various grain sizes, from the finest which is made to 1 micron (0-001 mm.).
- Absorption, Differential selective see pleochroism.
- Absorption, Selective the absorption of certain colours (wavelengths) from the incident white light when passing through a coloured medium. The colour of the medium results from the mingling of the colours which are not absorbed.
- Absorption Spectra the pattern of dark lines or bands seen when light which has passed through a gemstone is examined by a spectroscope.
- Accarbaar name applied to black coral. Also Akabar.
- Acetone an organic liquid which softens the cellulosic types of plastics and can therefore be of use in their distinction.
- Acetylene tetrabromide (tetrabromoethane) a liquid having a formula which may be used as a heavy liquid or as a medium in refractive index determination, S.G. = 2-95, R.I.=1-63.
- Achroite colourless tourmaline.
- Acicular crystals crystals which have a needle-like form, for example, the crystal inclusions in rutilated quartz (Venus hair stone).
- Acid rocks a subdivision of the igneous group of rocks. Generally of light colour, they contain a high content of silica (over 66 per cent). The acid rocks include the granites, syenites and pegmatites.
- Actinolated quartz Rock crystal with included crystals of green actinolite.
- Actinolite a member of the amphibole family of minerals, actinolite is an end member of the tremolite-actinolite. (Nephrite Jade, part) is a variety of actinolite while the fibrous variety is the asbestos of commerce.
- Acute bisectrix the line bisecting the acute angle between the optic axes in biaxial crystals.
- Adamantine the term used to describe a a type of luster , that is typical of diamond.
- Aaamantine spar name applied to silky brown sapphire.
- Adamas ("unconquerable") an ancient name for diamond.
- "Adelaide ruby" an undesirable name which has been applied to the almandine garnet found near Adelaide (Australia).
- Adularescence the name given to the opalescence seen in moonstone.
- Adularia variety of orthoclase feldspar of which moonstone is a gem variety.
- "African emerald" a MISNOMER ( COMMERCIAL LABEL ) applied to the green fluorite from South-West Africa. It must not be confused with the true emerald which is also found in South Africa.
- Agalmatolite a soft compact material used for carvings. It is a silica-rich variety of pinite, a decomposition mineral with variable composition, but approximating to muscovite (mica). Some agalmatolite is steatite, which see, and the hydrous aluminium silicate in compact form, known as pyrophyllite, is also termed agalmatolite.
- AgateAgate is a variety of Chalcedony Quartz and comes in many different color combinations. No two agates are alike. Varieties of agate include Blue, Blue Lace, Crazy Lace, Green, Indian, Moss, Tree, and Wood. Chalcedony (Agate) rates as a “Hardness 7” on the Mohs scale.
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AGS
American Gem Society – A professional jeweler’s society founded in 1934. AGS has a laboratory which grades diamonds and prepares a diamond grading report.
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AGS Diamond Cut Grade
The American Gem Society has developed a system for classifying cut quality. The AGS system uses a scale from 0 to 10, where Cut grade 0 is Ideal, 2 as Very Fine and 10 is the lowest grade and quality.
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AGTA
The American Gem Trade Association is the voice for the colored gemstone industry. Their Code of Ethics holds each Member to a high standard of professional business practices and a higher standard of enhancement disclosure than that required by the Federal Trade Commission.
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Alloy
An alloy is a mixture of two or more metals.back to top
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Amber
A delicate, fossilized tree resin. Amber is available in a wide array of colors, the most popular ranging from yellow to orange, mimicking the color of honey touched by the setting sun. Other less common colors of amber include red, green, blue, violet and black. Ranging from transparent to opaque, the finest amber is clear with little or no cloudiness.
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Amethyst
Amethyst is a member of the quartz family. Amethyst displays a majestic hue of purple, moving from very light to very dark. With purple being the chosen color of royalty, amethyst has long enjoyed popularity. The finest quality of amethyst exhibits a high degree of transparency and a rich deep purple color enhanced by flashes of burgundy or rose. Amethyst are most commonly found in Brazil, Uruguay, Canada and the United States (North Carolina). Amethyst is the birthstone for February.
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Anniversary Band
Typically given for wedding anniversaries, an anniversary band is a ring that is set with one or more rows of gems, usually diamonds. The diamonds may go completely, three quarters, or half way around the finger.
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Appraisal
An appraisal is a written estimate of the approximate retail replacement value of the item described. Appraisals can also be used for insurance purposes.back to top
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Aquamarine
Aquamarine is a member of the beryl family and is related to emerald in composition. The Greeks proclaimed this highly prized, light blue gem aquamarine, because it sparkles like the sea touched by the sun. Found in an array of pastel tones from very light to medium blue, aquamarine is often tinted by a splash of green. The delicate greenish blue of a fine aquamarine conjures up images of dancing light on tropical waters. Most aquamarines come from Brazil. Aquamarine is the birthstone for March.back to top
- Agatised coral fossil coral.
- Agatised wood see Chalcedony.
- AGS abreviation for American Gem Society.
- Ahrens prism a calcite prism used for the production of plane polarised light. It is essentially a modification of the Nicol prism designed to obtain a more economical use of calcite.
- Akabar name applied to black coral. See also Accarbnar.
- Alabaster a massive form of gypsum, see Gypsum.
- "Alabaster, Oriental" a MISNOMER ( COMMERCIAL LABEL ) for a stalagmitic variety of calcite characterised by well-marked banding. Another MISNOMER ( COMMERCIAL LABEL ) for this material is "Algerian Onyx".
- Alalite see Diopside.
- "Alaska black diamond" a MISNOMER ( COMMERCIAL LABEL ) for hematite.
- "Alaska diamond" a MISNOMER ( COMMERCIAL LABEL ) for rock crystal.
- Alasmoden pearls certain freshwater pearls.
- Albertite a jet-like mixture of hydrocarbons R.I. 1-55 ; S.G. 1-097; H. 2.5 Moderately insoluble in most organic solvents.
- Albite see Feldspar.
- Alcohol (ethyl alcohol) a volatile liquid. May be used for diluting certain heavy liquids and as an immersion liquid (R.I. 1-36).
- "Alencon diamond" a MISNOMER ( COMMERCIAL LABEL ) for rock crystal.
- Alexandrite see Chrysoberyl.
- Alexandrite-like synthetics suitable coloured synthetic corundums and spinels made to imitate the chrysoberyl alexandrite. See Manufactured gems.
- "Algerian oynx" a MISNOMER ( COMMERCIAL LABEL ) for a stalagmitic variety of calcite characterised by well-marked banding. Also known as "Oriental Alabaster".
- Allochromatic minerals minerals which are perfectly colourless when pure, but may be coloured by impurities, generally a metallic oxide which has no essential part in the chemical composition, or by sub-microscopic particles or inclusions of a coloured mineral, e.g., corundum when pure is colourless (white sapphire), when containing a trace of chromium oxide is red (ruby), titanium oxide giving a blue shade (sapphire), while iron gives greens and yellow shades (green and yellow sapphires). See also Idiochromatic minerals.
- Allotropic the name applied to the phenomenon shown by some chemical bodies of assuming different forms, e.g., carbon may form either diamond, charcoal or graphite.
- Alluvial deposits deposits of minerals which have been brought down by rivers and are found in their dried-up beds.
- Almandine a name applied to the iron-aluminium group of garnets.
- Almandine-Pyrope Series the isomorphous garnet series with end-members, pyrope, and almandine. Practically all red garnets belong to this series, being mixtures of pyrope and almandine molecules.
- "Almandine spine!" a name applied to the reddish-violet colour of gem spinel.
- Almandite see Garnet (Almandine).
- "Aloxite" trade name for an abrasive made of synthetically produced aluminium oxide.
- "Alundum" trade name for an abrasive made of synthetically produced aluminium oxide.
- Amatrix a name, a contraction of American matrix, applied to concretions of variscite in quartz (or chaleedony3. The material is usually cut with the green variscite as centre surrounded by grey, reddish or brownish quartz. S.G. about 2-6 with H from 5 to 6.
- Amazonite name applied to the green microcline feldspar, see Feldspar.
- "Amazon jade" a MISNOMER ( COMMERCIAL LABEL ) applied to the green microcline feldspar, see Feldspar.
- Amazon-stone see Feldspar (Microcline).
- Amber a natural resin hydrocarbon. R.I. 1 54; S.G. 1-03 to 1-10; H. 2 to 2.5; Amorphous; Colours, yellow, reddishbrown, bluish, whitish and black; Varieties, Succinite (North German), Roumanite (Roumania), Simetite (Sicily), Burmite (Burma).
- Amblygonite R.I. 1-611--1-637, S.G. 3-015 to 3- 033, H. 6. Triclinic. Colourless, yellow and pale mauve. Localities, Brazil, U.S.A.
- Ambroid see Pressed amber.
- American Gem Society a trade association of jewelers.
- "American jade" a MISNOMER ( COMMERCIAL LABEL ) for the massive green variety of idocrase. See Californite.
- "American ruby" a MISNOMER ( COMMERCIAL LABEL ) for garnet or rose quartz.
- Amethyst violet-coloured quartz, see Quartz.
- Amethystine quartz a massive quartz with patchy amethyst colouring. Sometimes used for small carvings.
- "Amethyst, Lithia" a MISNOMER ( COMMERCIAL LABEL ) for lilac spodumene.
- "Amethyst, Oriental" a MISNOMER ( COMMERCIAL LABEL ) for violet corundum.
- Amino plastics name applied to the urea and thiourea in formaldehyde condensation product. They are synthetic resins of the "bakelite" type.
- Amorphous (without form) material which has no definite internal structure and havings its properties the same in all directions.
- Amphibole the name applied to a group of minerals whose physical and chemical characters serve to link them together, in one family. They are silicates of iron, magnesium, calcium, sometimes sodium (rarely potassium), with or without silicate of aluminium. Nephrite (jade, part), asbestos and hornblende are amphiboles.
- Amygdule a rounded or almond-shaped gas cavity in volcanic rocks which later fills with mineral matter, often chalcedony.
- Amyl acetate a liquid having a refractive index of 137. The liquid is useful as a test for the cellulosic plastics which soften under its influence.
- Analcite R.I. 1-49; S.G. 2-22 -- 2- 29; H. 5-5.5 . Gem material is colourless. Localities, U.S.A., Italy, Czechoslovakia, Japan, Scotland, etc.
- Analyser the Nicol prism or "Polaroid" disc which is placed above the objective in the polarising microscope, see also Polariscope.
- Anatase R.I. 2-493 -- 2-554; S.G. 3-82 to 3-95; H. 5.5 to 6; Tetragonal; Colours, blue, brown to black; Localities, Switzerland, Brazil.
- Andalusite R.I. 1-633 --- 1-644; S.G. 3-1 to 3-2; H. 7 to 7.5; Rhombic; Colours, green, brown and red; Localities, Andalusia (Spain), Ceylon, Madagascar and Brazil. See also Chiastolite.
- Andradite see Garnet.
- Anglesite