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    Bacalite name applied to a variety of amber from Lower California, Mexico.

    Baguette-cut a modern style of cutting producing a long rectangular-shaped stone with parallel facets; sometimes called batons, both terms being French. See Cuts of stones, "Chart".

    Bakelite a synthetic resin sometimes used for imitations of gem materials. Two types (1) a condensation product of phenol (carbolic acid) and formaldehyde. R. I. 1-54 to 1-70 (usually 1-62 to 1-66); S.G. 1-25 to 2-00 (clear types 1-25 to 1-30). (2) Known as Amino Plastics. Urea replaces phenol in the composition. R.I. 1-55 to 1-62; S.G. 1-48 to 1-55.

    Bales Ruby a MISNOMER ( COMMERCIAL LABEL ) for the paler types of red spinel, which see.

    Ballas an important industrial variety of diamond. The stones are spherical masses of minute diamond crystals arranged more or less radially. They have no well-defined cleavage planes and thus have great resistance to abrasion. Found in Brazil and Africa. Spherical white or greyish diamonds which have cleavage planes are often called "ballas" although they should more correctly be called "bort".

    Barite (Barytes) S.G. 4-5; H. 3; Orthorhombic; Colourless, white, yellow, green, red, blue, or brown. World wide occurrence.

    Barium titanate This compound has been made synthetically and may at some time be produced as a gemstone. The S.G. is 5-90 and the R.I. 2-40.

    Baroque pearls name applied to pearls which are irregular in shape. Also known as Barrok pearls.

    Barrok pearls see Baroque pearls.

    Basic rocks the name applied to igneous rocks with less than 52 % of SiO,2. See Acid rocks.

    Bastite an altered enstatite; S.G. 2-6; H. 3.5 to 4; Colour, leek green; Locality, Harz Mountains.

    Bastard-cut a term used for fashioned stones which do not conform to the recognised typical forms, or which show some slight modification from the "pure" forms. The term applies only to those stones which have a regular and symmetrical arrangement of the facets; should they be irregular or haphazard the term Cap-cut is used.

    Batons an alternative name for stones cut in the baguette style. See Baguette-cut.

    Bayldonite R.I. 195-1-99 ; S.G. 4-35; H. 4.5; Monoclinic; greenish, S.W. Africa, Cornwall (England).

    Becke's test a method of refractive index determination.

    Beilby layer the name applied to the liquid-like layer of ultramicroscopic depth produced during the polishing of gemstones. It may be described as a local fusion at the minute projecting points on the nearly plane surface and the consequential spreading of a liquid-like layer over the entire surface. The nature of the polish layer may be divided into four groups:
    (1) The melting point appears too high for the production of a Beilby layer. The polishing process being merely a fine grinding, e.g., Diamond (and graphite).
    (2) The Beilby layer is amorphous (liquid-like) at the moment of formation, but immediately recrystallises in the same orientation as the underlying crystal structure, e.g., Quartz.
    (3) In which the Beilby layer recrystallises only on surfaceswhich approximate to important crystal planes (as cleavage surfaces and possible crystal faces), e.g., Calcite and Kyanite.
    (4) In which the Beilby layer remains amorphous on all surfaces, e.g., Spinel and Zircon.

    Bengal Amethyst a MISNOMER ( COMMERCIAL LABEL ) for purple sapphire.

    Benitoite R.I. 1-757 --- 1-804; S.G. 3-64 to 3-65 H. 6.5; Trigonal; Colour, blue; Locality, California.

    Benzene a liquid hydrocarbon used for dilution of heavy liquids of organic origin. S.G. 0-88.

    Bernat an amber imitation in plastic.

    Beryl R.I. 1-560 -- 1-565 to 1-590 --- 1-599 S.G. 2-65 to 2-85; H. 7.5 to 8; Hexagonal; Colours, grass green (Emerald), sea-green and sea-blue (Aquamarine), blue, violet, yellow (golden beryl or Heliodor), pink (Morganite), colourless (Goshenite); Localities, (emerald) Egypt, Colombia, Brazil, Ural Mountains (Russia), S. Africa, Rhodesia, India and Pakistan, Zambia, (aquamarine) Madagascar, Ural Mountains, Brazil and Ceylon, S.W. Africa. Fine blue aquamarines are most commonly the result of heat treatment.

    Beryl glass fused beryl which thereby loses its crystalline character and becomes a glass. S.G. 2-41 to 2-49, R.I. 1-50 to 1-52. This glass is sometimes used for green and blue imitation gems.

    BerylloIiite R.I. 1-552 --- 1-564 to 1-554 --- 1-566; S.G. 2-80 to 2-85; H. 5.5 to 6; Rhombic; Colour, colourless to pale yellow; Locality, Stoneham, Maine (U.S.A.).

    Beryloscope an instrument containing coloured glass dichromatic filters, acting similarly to the Chelsea colour filter.

    Bezel that part of a cut stone which lies above the girdle or setting edge. In the brilliant-cut stone it has the table facet and 32 surrounding facets. An alternative name is Crown.

    Bezel facets name applied to four of the eight large four-sided facets surrounding the table in the crown of a brilliant-cut stone. An alternative name is Templet.

    Biaxial the term used to describe the optical character of anisotropic crystals which have two directions of single refraction; confined to minerals belonging to the rhombic, monoclinic and triclinic crystal systems.

    Billitonite a natural glass (tektite) found in Billiton Island, in the Dutch East Indies, and Java, Borneo and Malaya. R.I. 1-51; S.G. 2-45. See Tektite.

    Birefringence Double refraction, the amount being measured by the difference between the maximum and minimum refractive indices in an anisotopic mineral.

    Bivalve molluscs the name applied to certain species of shellfish whose shelly covering consists of a pair of shells, slightly hollow on the inner side and hinged along one edge. e.g., oyster and mussel.

    Biwa pearls non-nucleated cultured pearls from Biwa Lake, Japan.

    Black coral a coral consisting mainly of conchiolin and is fished from Pacific waters. The material has a density of 1-34 and has a limited use in jewelry.

    Black diamond (a) crystalline diamond, black and virtually opaque, occasionally cut as a gem. (b) Carbonado.

    Black dyed opal a type of Australian opal which1 has been stained black to enhance the play of colour.

    Black garnet see Garnet (Andradite and Almandine).

    Black moonstone name applied to transparent labradorite. See Feldspar.

    Black opal a highly-prized opal found in New South Wales, Australia. The dark sandstone in which it is found, being rich in iron, being responsible for the depth of tint.

    Black pearls pearls of greyish, brownish or greenish black, found in the Gulf of Mexico and certain of the Pacific Islands. The cause of the colour is not clear but is thought to be due to the nature of the water in which the animal lives. Black pearls are occasionally imitated by polished spheres of haematite. Black clam pearls (q.v.) are not nacreous.

    Blende (Zinc-blende) R.I. 2-368 to 2-371; S.G. 4-08 to 4-10; H. 3.5: to 4; Cubic; Colours, yellowish-brown; Localities, Spain and Mexico. Blende has a high dispersion: 0-156.

    Blister pearls pearls which have been formed over an irritant which had become cemented to the shell of the mollusc. When removed the pearl has a rough back not covered by nacre which is generally ground flat and covered by the setting. These pearls are mostly of an irregular shape.

    Blond shell plain yellow tortoise-shell.

    Bloodstone a dark green chalcedony containing spots of red jasper, also called Heliotrope. See Chalcedony.

    Blue earth the glauconite sands in which amber is found in the North German deposits.

    Blue gold gold of bluish tint induced by the use of steel or iron as an alloy.

    Blue ground see Kimberlite.

    Blue John massive violet-blue and white banded fluorspar from Derbyshire, hence known as "Derbyshire Spar".

    Blue moonstone a MISNOMER ( COMMERCIAL LABEL ) for chalcedony stained blue.

    Blue-pearls really a lead-grey in tint, these pearls owe their colour to a large kernel of conchiolin.

    Blue-white a name applied to perfection colour in gem diamond. Open to abuse, it is not a satisfactory term.

    Boart, Boort, Bort, Bortz the name applied to a cryptocrystalline form of diamond, translucent to opaque and of a dark colour, and sometimes possessing a radial structure. Unlike "ballas" they possess a cleavage. Found in Africa, but a smaller production in Brazil, Venezuela and Guyana. Imperfectly crystallised diamond, lacking cohesive strength, multiple crystals, coated fragments, chips, etc., of various shapes and colours unfit for gems are called boars or Crushing boars, and are used for crushing into diamond powder.

    Bohemian diamond a MISNOMER ( COMMERCIAL LABEL ) for rock crystal.

    Bohemian garnet the name applied to the pyrope garnet found in Bohemia. These stones cut as roses were prevalent in Victorian jewelry. Many of these Bohemian pyropes show an absorption spectrum more reminiscent of the spinel than the usual spectrum seen in the almandine-pyrope series.

    Bohemian ruby a MISNOMER ( COMMERCIAL LABEL ) for red garnet.

    Bohemian topez a MISNOMER ( COMMERCIAL LABEL ) for yellow quartz.

    Bonamite see Smithsonite.

    Bone the hard material composing the skeleton or framework of mammalian animals sometimes used in the simulation of ivory. The material is distinguished from ivory by the difference in structure seen by the microscopical observation of a thin section or peeling.

    Bone turquoise see Odontolite.

    Boracite R.I. 1-66; S.G. 2-96; H. 7; Cubic; Pale green; Localities, U.S.A. and Germany.

    Borazon a cubic form of boron nitride a synthetic product made in the similar way as are synthetic diamonds. Said to be as hard as, or harder than diamond. H; 3-45, but it is only produced as microscopic crystals

    Boron carbide an artificially prepared high quality abrasive material. H 9.5 but usually considered to be harder than silicon carbide (carborundum).

    Bortz In U.S.A. specially refers to industrial diamonds while Bort is used for crushing purposes.

    Botryoidal forms When the surface of a mineral is covered with spherical protuberances due to areas of compact radially arranged fibrous crystals.

    Bottle-stone see Moldavite.

    Boule the pear-shaped mass of corundum or spinel as it comes from the oxy-hydrogen furnace used in the Verneuil process.

    Bowenite a hard variety of serpentine which simulates jade. R.I. near 1-56; S.G. 2-59; H. about 5; has been marketed under the MISNOMER ( COMMERCIAL LABEL ) "New Jade". Some bowenite may be stained.

    Brazilianite (Brasilianite) R.I. 1 598-1 617; S.G. 2-94; H. 5.5; Monoclinic; Colour, yellowgreen; Locality, Brazil and the U.S.A.

    Brazilian onyx a MISNOMER ( COMMERCIAL LABEL ) for banded calcite.

    Brazilian peridot a MISNOMER ( COMMERCIAL LABEL ) for yellow-green tourmaline.

    Brazilian ruby a MISNOMER ( COMMERCIAL LABEL ) for pink or "fired" topaz, or pink tourmaline.

    Brazilian sapphire a MISNOMER ( COMMERCIAL LABEL ) for either blue topaz or similar colour tourmaline.

    Brazilian topaz yellow topaz, see Topuz.

    Breccia a mass consisting of broken pieces of rock or mineral with angular edges which has been cemented together by secondary mineralization.

    Break facets name applied, in one form of nomenclature, to the 16 small triangular facets on the crown and edging the girdle, and to the 16 similar facets on the pavilion. They are the cross and skill facets. They are sometimes known as the halffacets or halves.

    Brewster's angle the angle at which light reflected from a transparent substance exhibits maximum polarisation. This depends upon the R.I. of the substance and R.I. = tan 8.

    Brilliant a term used for diamonds cut in the brilliant form.

    Brilliant-cut the most important style of cutting for the diamond. The cut consists of 58 facets, a table and 32 facets in the crown and 25 in the base or pavilion of the stone. In the case of large stones the number of facets may be increased. See Cuts of stones Chart.

    Brillianteerer the Dutch name applied to the diamond cutter who completes the final facets in a brilliant-cut stone.

    Briolette a drop-shaped stone covered with triangular facets. The cut may be considered as a modified double rose.

    Bristol diamonds a MISNOMER ( COMMERCIAL LABEL ) for rock crystal, see Quartz.

    Brittleness the tendency of a material to easy fracture.

    Bromoform S.G. 2-9; R.I. 1-59.

    Brom-toluene an organic liquid used for certain refractive index tests. R.I. = 1-55.

    Bronzite a mineral closely related to enstatite, which has a chatoyant bronzy lustre.

    Brookite R.I. 2-583 --- 2- 705; S.G. 3-87 to 4 08; H. 5.5 to 6; Orthorhombic; Yellowish, hair-brown and reddishbrown. Localities, France, Switzerland and U.S.A.

    Brown one of the classifications of gem diamond.

    Bruting the actual cutting of one diamond with another diamond, is employed whenever it is necessary to remove diamond rapidly and where finish is unimportant, since only a frosted surface is generated. Formerly a laborious hand operation but is now carried out by an electric eccentric chuck

    Bubbles the spherical, oval or tadpole-shape`] inclusions of gas seen in some synthetic stones and most glasses (pastes). They may also be seen in natural and synthetic resins. Also seen in liquid-filled cavities in emerald, topaz, quartz and many other natural minerals.

    Buddstone a massive opaque green quartz from South Africa. Used as an ornamental stone.

    Burmite name applied to the amber found in Burma.

    Button pearls pearls having a rounded top and a flat base.

    Bye or Byewater a term used for diamonds tinged with yellow, stones being termed "first bye" or "second bye" according to the amount of yellow color.

    Byon the native name for the gem-bearing ground of Upper Burma.