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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

    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.

    Agate see Chalcedony.

    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 R.I. 1-877 --- 1-894; S.G. 6-30 --- 6-39; H. 3. Orthorhombic; White and yellow; Localities, U.S.A. and Scotland.

    Angstrom Unit the unit used for the small measurements required in the electro-magnetic spectrum below the infra-red, it is the ten-millionth part of a millimetre.

    Anhedral Crystals crystals which do not show good outward form.

    Aniline a liquid having R.I. 1-58, useful as an immersion medium.

    Anisotropic a term for crystals which exhibit double refraction, i.e., break up a ray of light into two rays which move with different velocities within the crystal. See also, Ordinary ray and Extraordinary ray.

    Anomalous double refraction double refraction in isotropic material, as seen by irregular extinction when viewed between crossed nicols. Due to internal strain.

    Anorthite see Feldspar.

    Antigorite a green serpentine resembling jade.

    Antilles pearl a type of "pearl" cut from the shell of the sea snail.

    Anyolite a green zoisite rock containing large opaque ruby crystals. Used as an ornamental stone. Found in Tanzania

    Apache tears obsidian.

    Apatite S.G. 3-15 to 3-22; H. 5; Hexagonal; Colours, blue-green (Moroxite), yellow-green (Asparagus stone), pink, violet, purple, blue (sometimes chatoyant) and colourless; Localities, Saxony, Bohemia, Maine (U.S.A.), Ceylon and Burma.

    Aplite a sugary-textured white to grey granite containing silvery muscovite. Used for statuary carving.

    Apophyllite S.G. 2-3 to 2-4; H. 4.5 to 5; Tetragonal; Colours, white, grey, yellowish, greenish, and flesh red; Localities, Harz Mountains (Germany), India, Sweden, Tyrol and Transylvania.

    Aquamarine see Beryl.

    "Aquamarine, Brazilian" a MISNOMER ( COMMERCIAL LABEL ) for blue topaz.

    "Aquamarine, Siam" a MISNOMER ( COMMERCIAL LABEL ) for the heat-treated blue zircon.

    "Aquamarine, Synthetic" a MISNOMER ( COMMERCIAL LABEL ) for the sea-blue or sea-green colours of synthetic corundum or spinel.

    Aqua regia a mixture of the powerful nitric and hydrochloric acids in the proportion of one of nitric to two of hydrochloric used as a solvent for gold.

    Aragonite S.G. 2-93; H. 3 to 3.5; Rhombic; Colour, colourless and white; Localities, Aragon (Spain), Bohemia, Sicily, Alston Moor (England), U.S.A., Germany and Hungary. This mineral is the major constituent of pearl.

    Aragonite a yellow stalagmitic calcite from South-West Africa.

    Arizona Ruby a MISNOMER ( COMMERCIAL LABEL ) for pyrope garnet found in Arizona.

    Arizona Spinel a MISNOMER ( COMMERCIAL LABEL ) for red garnet.

    Arkansas Diamond a MISNOMER ( COMMERCIAL LABEL ) for rock-crystal.

    Artificial resins general name applied to the synthetic products known as plastics. See Plastics.

    Artificial stones imitations of gem stones.

    Artificial treatment of gemstones anything that has been done by man to enhance the color, clarity or quality of a stone.

    Asparagus stone see Apatite.

    Asterias stones exhibiting a four, six or twelve-rayed star of light when cut en-cabochon in the correct crystallographic direction. Generally seen in corundums (star rubies and star sapphires with either six or twelve rays) and with rose quartz (generally six rays). Some garnets may also show the effect usually with four rays but if cut in certain directions may show six rays. Star corundums are made synthetically.

    Asterism a reflection from fibres or fibrous cavities in a stone, cut en-cabochon with its base parallel to the basal plane of the crystal, in a similar manner to chatoyant stones (see Chatoyancy) but having three sets of fibres crossing at angles of 60 (hence a six-rayed star), or at 90 (a four-rayed star). See also Diasterism and Epiasterism.

    Atom a unit which is the smallest part of a chemical element which remains unchanged during all chemical reactions. Although partly composed of electrically charged units such as electrons, protons, etc., atoms as a whole are electrically neutral.

    Atomic diamonds see Irradiated diamonds.

    Atomic weight the weight of the atom of an element compared with the weight of an atom of oxygen taken as 16. See A table of atomic weights.

    Augelite R.I. 1-57 --- 1-588; S.G. near 2-7; H. 5; Monoclinic; Colourless; U.S.A. and Bolivia.

    Australite a name applied to the button-shaped pieces of natural glass found in the south of Australia and Tasmania. See also Tektite.

    Autoclave a thick walled steel cylinder provided with a removable cover at the top to contain mineral saturated water at fairly high pressures. Used in the hydrothermal method of producing synthetic stones.

    Aventurine feldspar see Feldspar (Sunstone).

    Aventurine glass a glass made with included copper crystals to produce an imitation of the yellow and red aventurine quartz. An alternative name for this imitation is "Goldstone". Now made in a blue colour.

    Aventurine quartz Quartzite with iridescent spangled effect due to green mica or to reddish iron minerals. There is also a grey aventurine quartz which is again due to some form of mica.

    Axes, Crystallographic The optical direction of a plane in a stone.

    Axe-stone see Nephrite.

    Axinite R.I. 1- 67 --- 1-684; S.G. 3-27 to 3-29; H. 6.5 to 7; Triclinic; Colours, brown, honey-yellow and violet; Localities, France and Tasmania, also Cornwall (England), near Ottawa (Canada) and Pennsylvania, New York and Baja California (Mexico).

    Axis of symmetry the axis about which rotation of a crystal will cause it to occupy the same position in space more than once in a complete turn. The terms applied to the different classes of axes are: Twice; two-fold, died, half-turn or digonal axis. Three times; three-fold, triad, one-third-turn or trigonal axis. Four times; four-fold, tetrad, quarter-turn or tetragonal axis. Six times; six-fold, hexed, one-sixth-turn or hexagonal axis.

    Axis, Optic see Optic axis.

    Azure quartz Siderite, see Quartz.

    Azurite R.I. 1-730 --- 1- 838; S.G. 3-77 to 3-89; H. 3.5; Monoclinic; Colour, blue; Localities, Russia, Chile, South West Africa, Arizona (U.S.A.), and (:hessy (France). An alternative name is Chessylite.

    Azurmalachite an ornamental stone consisting of intimate association of azurite and malachite.