WinJewel is a complete program to run a retail jewelry store. Click on "Home" above to go to our start page. This jeweler's dictionary is provided as a free service by WinJewel.

Click on the letter of the word you want:


    Mabe pearls cultured blister pearls in which the original nucleus has been removed and replaced by a smaller bead cemented in with white wax and the pearl completed with a dome-shaped backing piece of mother-of-pearl.

    Macles flat, triangular twin crystals of the octahedron. Term used for diamond crystals of this type.

    Madagascar aquamarine a blue beryl from Madagascar, showing strong dichroism.

    "Madeira topaz" a MISNOMER ( COMMERCIAL LABEL ) for citrine.

    Magma deep seated molten material from which igneous rocks form.

    Magnesite R.I. 1 52-1 72; S.G. 3 0 to 3 12; H. 4; Trigonal; White; World wide, but Brazil is important.

    Magnetic spectrum see Electro-magnetic spectrum.

    Malachite R.I. 1 65-1 90; S.G. 3 74 to 395; H. 32; Monoclinic; Colour, green; Localities, Ural Mountains (Russia), Chile, Rhodesia, U.S.A., Katanga (Belgian Congo).

    Malacolite see Diopside.

    Mammoth ivory fossil ivory from the tusks of the mammoth (Elephas primigenius), found in Siberia. And from allied animals in North America. See Fossil ivory.

    Manganese dioxide a black powder sometimes used as a polishing agent.

    Mantle the cellular epithelial tissue of the pearl producing molluscs; that part of the animal which secretes the nacre.

    Manufactured stones synthetic stones, see Chart 167.

    Maori stone name for nephrite from New Zealand.

    Marble a massive form of crystalline limestone. See Calcite.

    Marcasite S.G. 4-8; H. 6 to 6.5; Rhombic; Colour, metallic grey yellow (this is a mineral dimorphous with pyrites); "Marcasite" in the trade is really pyrites, or often merely cut steel or white metal.

    "Marmora diamond" a MISNOMER ( COMMERCIAL LABEL ) for rock crystal.

    Marquise a stone cut on the brilliant style with the exception that the outline is boat-shaped instead of having a circular form.

    "Mass aqua" the popular name for a special hard glass imitation of aquamarine.

    Massive a term used for minerals without definite crystal form, or composed of masses of small crystals.

    Matrix the mass of rock in which minerals and crystals are found. Turquoise and Opal are often cut with some of the matrix. Also called Mother rock.

    "Mature diamond" a MISNOMER ( COMMERCIAL LABEL ) for the colourless (fired) zircon.

    Maw-Sit-Sit the name applied to a jadeite-albite rock found in Upper Burma.

    Maxixe-aquamarine, Maxixe-beryl a blue beryl showing strong dichroism, from the Maxixe mine, Minas Gerais, Brazil.

    "Medina emerald" a MISNOMER ( COMMERCIAL LABEL ) for emerald green glass.

    Medium the term applied to any material, solid, liquid or gaseous, through which light passes. The medium may not necessarily be transparent for even in opaque substances light may penetrate to a very small depth.

    Meerschaum R.I. mean 1-55; S.G. 1-0 to 2-0 H. 2 to 2.5; Monoclinic; Colour, creamy white; Locality, Asia Minor. Also known as Sepiolite.

    Melange term used for diamonds of mixed sizes but larger than .25 carat in weight.

    Melanite a black variety of andradite. See Garnet.

    Melee small diamonds of mixed sizes, less than .25 carat in weight.

    Melinophane R.I. 1-59 --- 1-61; S.G. 3-0; H. 5; Tetragonal; Yellow; Norway.

    Menilite alternative name for liver opal. See opal.

    Mercury-vapour lamp an electric discharge lamp producing an intense bluish light rich in ultra-violet rays. It is operated by the arcing of mercury vapour in a vacuum tube which is generally made of quartz glass.

    Mesolite a sodium calcium aluminium silicate ; R. l. 150 ; S.G. 2 29; H. 5; Monoclinic; White or colourless (fibrous) World wide occurrences.

    meta-made an artificial stone made in Japan. It resembles, and has properties near to, jade.

    Metamict the term used for material which has suffered a break-down from a crystalline to an amorphous state; common in minerals containing radio-active elements, it is the name applied to the "low" type of zircon which has decomposed into nearly amorphous SiO2 and ZrO2 from the "normal" fully crystalline zirconium silicate. Stones of this type, mostly found in Ceylon, are nearly singly refracting and generally green in colour. Prolonged heating returns these stones to the "normal" type.

    Metamorphic rocks are those formed from igneous or sedimentary rocks by the action of heat and pressure.

    Methylene iodide a liquid used for immersion purposes in the microscopical examination of gemstones, for certain refractive index tests and as a heavy liquid. R.I. 1 74; S.G. 3 32.

    Methylene iodide and dissolved sulphur a mixture used as a refractometer contact liquid and as an immersion liquid in certain refractive index tests. R.I.= 1 78.

    Methylene Iodine, dissolved sulphur and tetraiodoethylene a highly refractive liquid used as a refractometer contact fluid and as an immersion liquid in certain refractive index tests. R.I. = 1 81.

    Methylene iodide with dissolved iodine and iodoform a highly refractive liquid used as a refractometer contact fluid and as an immersion liquid in certain refractive index tests. R.I. depends on mixture

    Metric carat the legal weight unit for gemstones, one-fifth of a gramme. See Chart 224.

    "Mexican diamond" a MISNOMER ( COMMERCIAL LABEL ) for rock crystal.

    "Mexican jade" a MISNOMER ( COMMERCIAL LABEL ) for green-dyed calcite.

    "Mexican onyx" a MISNOMER ( COMMERCIAL LABEL ) for banded calcite.

    Mexican water opal a variety of Opal which shows a play of colour in a practically transparent body.

    Nlica schist a general term for a laminated rock in which mica is an abundant ingredient.

    Micro chemical tests tests carried out by the observation of chemical reactions on minute portions of a mineral. A scraping of the substance to be examined being placed on a glass slip and the reactions to various reagents studied under the microscope.

    Microcline see Feldspar.

    Microlite 1-93; S.G. 5-5; H. 5.5; Cubic; Brownish-green, yellowish-brown to hyacinth-red; Elba and U.S.A.

    Micron a unit of measurement for small sizes. It is 0 001 mm. and is used in the measurement of the grains in diamond powder.

    Microscope an instrument consisting of a system of lenses fitted into a tube which can be raised or lowered for focusing, which is used to give a greatly enlarged image of an object. A petrological microscope contain$ in addition, two nicol prisms, in order that observations may be made in polarised light.

    Milk-opal see Opal.

    Milky quartz crystalline quartz of a milky white colour When containing gold, is termed "gold quartz".

    Mineralogy the science which deals with minerals.

    Mineral species a homogeneous substance produced by the processes of inorganic nature, having chemical composition, crystal structure, and physical properties which are constant within narrow limits.

    Mixed-cut a style of fashioning gem stones. Used to denote an unusual cut.

    Minimum deviation the position of two facets forming a prism, in relation to a beam of light, where the beam is passing through them symmetrically, or in other words, with least deviation. (For Refractive index determination by the method of minimum deviation, see Chart 129.)

    Mocha stone chalcedony with dendritic inclusions.

    Moe's gauge a diamond gauge on the principle of calipers, which by measuring across the diameter of the stone and also its depth and referring to tables it is possible to estimate the weight of the stone.

    Mohs' scale a scale of the hardness (H) of minerals. 10 is the hardest with 1 being the softest.

    "Moiave moonstone" a MISNOMER ( COMMERCIAL LABEL ) for lilac-tinted chalcedony from the Mojave Desert, California.

    Moldavite a silica glass found in Bohemia and Moravia and not unlike obsidian. R.I. 1-48 to 1-50; S.G. 2-3 to 2-5; H. 5.5; Amorphous; Colour, light to dark green, rarely brown; Alternative names, "Water chrysolite" and "Bottle-stone".

    Molecular weight of a substance is the sum of the atomic weights of the atoms composing a molecule oi the substance, e.g., the atomic weight of calcium is 40, of carbon 12, and of oxygen 16; therefore the molecular weight of calcite , composed of one atom of calcium, one of carbon and three of oxygen, is 40+12+(3 x 16) = 100.

    Molecule a group of two or more atoms in close combination. The smallest quantity of an element or compound which can exist alone.

    Mollusc a member of the sub-kingdom of soft bodied, and usually hard-shelled, animals, as the oyster, scallop, mussel, etc.

    Momme a Japanese weight used in the marketing of cultured pearls. 1 momme=3.75 grams= 18.75 carats=75 pearl grains.

    Monobromonaphthalene (x type) a liquid used as an immersion fluid in the microscopical examination of gemstones, and in certain refractive index tests. R.I. 1-66; S.G. 1-49; B.P. 279 C.

    Monochlorbenzene a liquid having a value in certain refractive index tests. R.I.= 1 53.

    Monochlornaphthalene a liquid having a value in certain refractive index tests. R.I.= 1 63.

    Monochromatic light light of one wave-length only. In practice it is usual to employ the yellow glow of sodium vapour.

    Monoclinic one of the crystal systems. See Chart 1 13.

    "Montana ruby" a MISNOMER ( COMMERCIAL LABEL ) for red garnet.

    "Mont Blanc ruby" a MISNOMER ( COMMERCIAL LABEL ) for rose quartz.

    Moonstone see Feldspar.

    Morallons a name locally used in the Colombian emerald mines for inferior stones. See Canutillos.

    Morganite rose-coloured beryl, see Beryl.

    Morion a black variety of smoky quartz.

    Moroxite see Apatite.

    Mortar a bowl-shaped vessel of agate or earthenware in which minerals are powdered by the aid of a club-shaped instrument known as a pestle. A variation consisting of a hollow steel body into which loosely fits a steel pestle, is used for reducing diamond to powder.

    Moss agate chalcedony with dendritic inclusions.

    Mossy stones stone rendered cloudy by fissures. Mostly referring to emeralds.

    "Mother of emerald" a MISNOMER ( COMMERCIAL LABEL ) for prase.

    Mother-of-pearl the iridescent nacreous material from the shells of molluscs.

    Mother rock see Matrix.

    "Mountain jet" a MISNOMER ( COMMERCIAL LABEL ) for black obsidian.

    "Mountain ruby" a MISNOMER ( COMMERCIAL LABEL ) for red garnet.

    Multi-facet diamond a term used to describe a diamond with the girdle polished or faceted. The term is American, and application has been made to use it as a trade mark.

    Mussel pearls pearls obtained from the freshwater mussel. The most important species in Europe is Unio margaritifera. In the U.S.A. the genus Quadrula supplies such pearls.