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    "Radiant" suggested, but undesirable name for the synthetic colourless spinel. Another of these fancy pseudonyms for this synthetic spinel is Corundolite.

    Radiant cut a cut of diamond that has a rectangular outline like an emerald cut but the facet placement more approaching the arrangement found on a brillant cut.

    Radium diamond,71 a MISNOMER ( COMMERCIAL LABEL ) for smoky quartz.

    Radium-treated diamonds Diamonds when irradiated, that is kept adjacent to radium bromide for some time, assume a Green colour which is fairly permanent. This is due to bombardment by the alpha particles of the radium. These treated stones are radio-active and can be distinguished from natural stones of a green colour by their ability to fog a photographic film.

    Reconstructed stones stones made by fusing together small pieces of real crystal to make a larger stone, care being taken to ensure crystallisation and better colour obtained by the addition of colouring oxide. Was usually confined to the making of ruby. Now superseded by the synthetic gem.

    Red gold an alloyed gold showing a redder colour than the normal yellow gold. It is often used for contrast and is made by alloying with copper alone, or copper and silver in the proportion of three to two.

    Reduction the term applied to the chemical change in which the oxygen or other non-metal is taken away from a compound.

    Reflection of light a ray of light striking a polished surface is reflected from it in accordance with the following laws: (a) the angle of reflection is equal to the angle of incidence. (b) the incident ray, the reflected ray and the normal at the point of incidence are in the same plane.

    Reflectometer alternative, and incidentally more correct name for refractometer.

    Refraction of light a ray of light passing from a medium to one optically denser is bent towards the normal, and similarly in passing into a medium less dense is bent away from the normal. This bending is in accordance with definite laws. See Snell's Law, Chart 128.

    Refractive index the speed of light in a gem stone as a relation to the speed of light in a vacuum. Used as a non-distructive test to identify gems.

    Refractometer an optical instrument arranged to show the critical angle of total reflection as a shadow edge, on a scale calibrated in refractive indices. In the case of the better class instruments used in laboratories the position of the shadow edge is read oR on a graduated arc. There are different types which may use highly refractive glass, synthetic spinel or diamond for the prism or hemisphere.

    Relative density alternative term for specific gravity. More usually used for liquids. See Density and Specifie gravity, Chart 117.

    Resin Opal see Opal.

    Rhinestonea name applied to the transparent paste which, colourless in the main, shows patches of various colours.

    Rhodium S.G. 12-44; a white metal, nearly the same colour as platinum, used for plating. This rhodium plating process is used to improve the colour and general appearance of gem-set jewelry.

    Rhodizite a borate of aluminium and caesium; R.I. 169; S.G. 3 40; H. 8; Cubic; Colours, pale green and pale yellow; Locality, Madagascar. Very rare.

    Rhodochrosite R.I. 1-597 --- 1-817 to 1-605 --- 1-826; H. 4; S.G. 3-45 to 3-70 for the rose red material, rising with increase of iron; Trigonal; Colour, rose-red; presence, by replacement of iron, calcium and magnesium, introduces shades of yellow and brown; Localities, Hungary, Saxony, Colorado U.S.A. and Argentina. Inca rose and Rosinca are fancy trade names for this material.

    Rhodolite see Garnet.

    Rhodonite R.1. 1-71--- 1-73 to 1-72 --- 1-75; S.G. 3-5 to 3-7; H. 5 to 6; Triclinic; Colours rose-red and pink (opaqued; Localities, Russia and U.S.A. small clear crystals found at Wermland in Sweden are occasionally cut.

    Rhombic (Orthorhombic, Trimetric) one of the crystal systems. See Chart 1 13.

    Rhombic dodecahedron the geometric solid with twelve rhomb-shaped faces. A crystal form of garnets and some diamonds.

    Rhombohedral see Trigonal.

    Rhombohedron a solid bounded by six rhombohedral faces; a common form in trigonal crystals.

    Ribbon jasper jasper in which the colours run in stripes.

    River pearl natural pearl from freshwater mussels.

    Rock-crystal see Quartz.

    Rose quartz see Quartz.

    Roses the name applied to small diamonds cut in the rose-cut style.

    Rosinca a fancy name for Rhodochrosite.

    Rosolite see Xalostocite.

    Rottenstone a soft, friable, very finely textured earthy mass used as a polishing compound. The material is a residual product from the weathering and decaying of a siliceous, argillaceous limestone.

    Rouge the red oxide of iron used as a polishing medium. Green rouge is chromium oxide.

    Roumanite Roumanian amber. See Amber.

    Royal-cut A modern cut for diamond using a greater number of facets.

    "Rozircon" a MISNOMER ( COMMERCIAL LABEL ) for the rose coloured synthetic spinel.

    Rubasse a spangled red variety of quartz or rock crystal coloured by the inclusion of minute blood-coloured scales of oxide or iron. The natural stone is rare and is found in Brazil. This stone may be imitated by cracked quartz which has had red dye introduced along the cracks.

    Rubbish a mining classification for diamonds which can only be used for making powder.

    Rubellite see Tourmaline.

    Rubicelle see Spinel.

    Ruby see Corundum.

    "Ruby, Adelaide" a MISNOMER ( COMMERCIAL LABEL ) for red garnet.

    "Ruby, Arizona" a MISNOMER ( COMMERCIAL LABEL ) for the red garnet.

    "Ruby, galas" a MISNOMER ( COMMERCIAL LABEL ) for the pale red spinel.

    "Ruby, Bohemian" a MISNOMER ( COMMERCIAL LABEL ) for red garnet.

    "Ruby, Brazilian" a MISNOMER ( COMMERCIAL LABEL ) for rose-red (fired) topaz.

    "Ruby, Cape" a MISNOMER ( COMMERCIAL LABEL ) for the red garnet from South Africa.

    "Ruby, Colorado" a MISNOMER ( COMMERCIAL LABEL ) for red garnet.

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

    "Ruby, Siberian" a MISNOMER ( COMMERCIAL LABEL ) for rubellite. See Tourmaline.

    "Ruby Spinel" a MISNOMER ( COMMERCIAL LABEL ) for red spinel.

    Ruin marble a yellow marble with sections of a brown colour, due to the infiltration of iron.

    Ruthenium S.G. 12-3; a metal which, through belonging to the platinum group, has so far had no application in jewelry.

    Rutile R.I. 2-62 --- 2-90; S.G. 4-2 to 4-3; H. 6 to 6.5; Tetragonal; Colours, blood red, reddish-brown and black; Localities, Russia, Scandinavia, Italy, France, U.S.A., Switzerland, Madagascar and Brazil. Rutile is made synthetically by a modified flame fusion process. The colours produced are yellowish-white, yellow, orange, red and blue, the latter are very rare. They have similar constants to the natural rutile.

    Rutilated quartz clear rock-crystal with included crystals of rutile (see also Sagenitic Quartz Venus' hair stone).