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- Sagenitic quartz rock crystal with included crystals of rutile. See Quartz.
- Sapphire see Corundum.
- "Sapphire, Brazilian" a MISNOMER ( COMMERCIAL LABEL ) for blue tourmaline, or similar coloured topaz.
- "Sapphire, Lux" a MISNOMER ( COMMERCIAL LABEL ) for iolite.
- "Sapphire, Lynx" a MISNOMER ( COMMERCIAL LABEL ) for the pale blue shade of iolite.
- "Sapphire, Spinel" a MISNOMER ( COMMERCIAL LABEL ) for blue spinel. See Spinel and Ruty spinel.
- "Sapphire, Water" a MISNOMER ( COMMERCIAL LABEL ) for the dark blue shade of iolite.
- Sapphirine a term variously applied to the blue spinel or to the blue quartz. It is a name better dropped.
- Sard and Sardonyx see Chalcedony.
- Sark Stones Amethyst found in the island of Sark in the Channel Islands. Very little found to-day.
- Satin-spar fibrous white or pink calcite, or similar gypsum.
- Saussurite a decomposed feldspar; S.G. 3 2 (about); H. 61 to 7; Colour, greenish-gray to white; Locality, Switzerland. Sometimes simulates jade.
- Sawing a method whereby a diamond may be cut into two or more parts in directions other than the cleavage directions. It is carried out by the use of a diamond saw, a phosphorbronze disc fed with diamond powder and olive oil, and running at about 5,000 r.p.m. The same process is used also for the cutting of the less hard gemstones.
- "Saxony diamond" a MISNOMER ( COMMERCIAL LABEL ) for colourless topaz.
- Scapolite an isomorphous mixture of marialite and meionite R.I. (blue) 1-544 --- 1-560 (pink and yellow), 1-548 --- 1-570; S.G. 2-61 to 2-70; H. 6.5; Tetragonal; Colours yellow, pink (chatoyant), blue (chatoyant); Localities, Burma Madagascar and Brazil.
- Scaife a name applied to the cast-iron lap, which is 10" to 12" in diameter and used in diamond polishing. It must have an open porous structure and is provided with a paste of olive oil and diamond dust upon which diamonds are polished.
- Scheelite S.G. 5-9 to 6-1; H. 4 to 5; Tetragonal; White yellow, brownish to orange. Most of the gem material comes from the U.S.A. and Sonora, Mexico. Scheelite does not fluoresce under the long-wave ultra-violet lamp but glows with a blue colour under the short-wave lamp. Also made synthetically.
- Schiller the silver shimmer of light seen just below the surface of a stone and due to lamellar twinning, best seen in bronzite and moonstone.
- Schist a foliated and fissile metamorphic rock of layers of different minerals.
- Schorl black tourmaline.
- Scisscor-cut a variation of the trap cut in which the side facets surrounding the table are cut as elongated triangular facets. Also called Cross-cut. See Cuts of stones, Chart 181.
- "Scotch Topez" a MISNOMER ( COMMERCIAL LABEL ) for citrine, smoky quartz or cairngorm.
- Seed pearls very small pearls.
- Selenite the crystallised form of gypsum, generally found in well-formed monoclinic crystals. See Gypsum.
- Semi-precious stones An unsatisfactory term for all gemstones other than those mentioned as being "Precious stones". It is a term now discontinued by general consent.
- Senaille the name applied to small chips of diamond with irregularly polished facets set into jewelry. Often erroneously called `'roses".
- Sepiolite see Meerschaum.
- Serpentine R.I. 1-50 to 1-57 (mean); S.G. 2-50 to 2-65; H. 2.5 to 4; Monoclinic; Colours, greens, etc.; varieties, Williamsite, Bowenite, and Verd Antique may resemble jade. Bowenite is unusual in having hardness 51 to 6.
- Setting edge an alternative name for the girdle.
- Shagreen a material sometimes used as a covering to cigarette cases, lighters, mirrors, brushes and small boxes, etc. Originally made from the skin of the wild ass, which even now, with that of the horse and camel, provides much of the material. Shagreen is now generally derived from the skins of certain sharks and ray fishes. The material is dyed to suitable colour, generally green, blue, red and black.
- Shatter marks see Fire marks.
- Shattuckite R.I. about 1-80; S.G. about 3-8; H. 3: to 4; Monoclinic (massive); Blue; U.S.A. Its status as a mineral species has been disputed.
- Sheen a shimmering effect, due to reflection of light from a position inside the stone, in contradistinction to "lustre" which is a surface reflection.
- Shell-marble a marble consisting mainly of fossil shells.
- Shipley colorimeter an instrument for the colour grading of diamonds.
- "Siam aquamarine" a MISNOMER ( COMMERCIAL LABEL ) for the heat-treated bluish green zircon.
- "Siberian ruby" a MISNOMER ( COMMERCIAL LABEL ) for rubellite. See Tourmaline.
- Siberite a name used for violet tourmaline.
- Siderite blue quartz.
- Silica-glass R.I. 146; S.G. 221; H. 6; Amorphous; Colour, pale greenish yellow; Locality, Libyan Desert. A celestial origin is suggested by some authors, others regard it as sandstone fused by intense heat of basaltic intrusions. See also Quartz glass.
- Silicates formerly thought of as salts of various silicic acids. Now considered as compounds in which the structure is largely determined by the silicon-oxygen linkages which form the framework of the crystals. Examples are; Beryl, Spodumene, Zircon.
- Silk the whitish sheen seen in some corundums and due to the presence of vast numbers of microscopically small canals reflecting the light. "Pseudo-silk" is understood to be due to microscopic acicular crystals of titanic iron and is often observed in Siam stones.
- Sillimanite see Fibrolite.
- Simetite Sicilian amber, see Amber.
- Silver S.G. pure 10-5, standard 10-31; a lustrous white metal, malleable and ductile used in jewelry and for ornamental and utility articles. Standard silver has 925 parts of pure silver with 75 parts of alloy to the 1,000.
- Silver Cape a classification of diamond.
- Sine of angle the ratio between the side opposite that angle and the hypotenuse. The hypotenuse being the side opposite the right angle of a right angled triangle.
- Sinhalite R.I. 1-67 --- 1-71; S.G. 3-47 to 3-49; H. 6.5; Orthorhombic; Yellow and brown; Ceylon, Burma. A stone known for years as brown peridot and not discovered as a new mineral until 1952.
- "Sira" trade name for an abrasive, made of aluminium oxide artificially manufactured.
- Skew facets see Crossfacets.
- Skiagram an X-ray shadow photograph produced by radiations which have passed through the substance under examination. It depends upon the differing degrees of transparency of the various parts of the substance and is the method used in medical diagnosis. The method is used for the detection of cultural pearls.
- Skill facets are the eight small triangular facets around the girdle edge of the crown in the brilliant cut. They are adjacent to the cross or skew facets. The combined 16 facets, the eight cross and the eight skill, are often collectively known as break facets, half facets or halves.
- Slate; an argillaceous sedimentary rock of grey colour. It is used for the so-called "black marble", which early in this century was ated by heat.
- Sparklite a name which has been applied in the U.S.A. to the colourless (fired) zircon.
- Specific gravity The weight of a gem stone as a relation of the same volumn of water. Arrived at by weighing the stone out of water and weighing the stone in water then expressing the Specific Gravity as a relationship of these two weights. Used as a non-distructive way of identifing gemstones.
- Specific gravity bottle or Pyknometer a small flask fitted with a ground glass stopper pierced lengthwise with a capillary opening so that the bottle can be filled to a definite mark. It is used for the determination of the density of liquids, powders and small fragments by the direct weighing method.
- Spectra plural of spectrume.
- Spectrograph an instrument arranged for the production of spectra as in a spectroscope, but having a camera fitted in place of the telescope of the latter instrument so that a plate exposed in it will record, after development, the spectral lines (in bright line emission spectra) or the sections and bands preferentially absorbed (absorption spectra). Quartz prisms and lenses are used in order to obtain results in the ultra-violet region.
- Spectrolite labradorite feldspar found in Finland.
- Spectrometer an instrument used for the measurement of the spectrum. There are various types which may either allow the wave-length to be read off directly or to be arrived at by computation. The most usual types used in gemmological work are the direct vision direct reading types (Beck), and the table instruments consisting of a fixed collimating tube, to parallelise the light, and fitted with an adjustable slit, a graduated circular table upon which the crystal or stone is mounted, and lastly a telescope which may be moved round the table and to which a vernier is attached in order accurately to measure the angles. This is the instrument generally used in determining refractive index by the method of minimum deviation.
- Spectroscope an instrument which analyses a ray of light into the spectrum colours, and may be one of two types:
- (A) the prism type, where dispersion is effected by the different refringence of the glass prism for rays of different wave-length (colour).
- (b) diffraction grating type, where a grating of many fine parallel lines performs a similar function by a process of interference the effects being viewed by a lens system (a short telescope).
- Spectrum, Absorption the field seen in a spectroscope (or photograph, if spectrograph is used) when a source of white light from an incandescent solid is viewed by the instrument after suffering absorption by transmission through or reflection from a gemstone or other medium. Owing to the absorptionoflight by the medium being examined,darkbands or lines indicating the wave-lengths absorbed, may be seen across the otherwise continuous spectrum. This often gives useful information of a diagnostic nature. See Chart 147.
- Spectrum, Emission the field seen in a spectroscope (or photograph if spectrograph is used) when a source of light is examined by the instrument. It may be one of three kinds:
- (a) Continuous; the familiar rainbow colours, a continuous graduation of light passing imperceptibly through red to violet. It is produced by incandescent solids.
- (b) Swan; a fluted or banded formation of bright lines, each of which appears to be sharp towards the side of longer wave-length and to fade away on the opposite side (actually a group of very fine lines comparatively far apart on one side and crowded closer and closer together towards the other until they are so dense that they appear one line at the heady; produced by the incandescent vapours of compounds.
- (C) Bright Line; a number of sharp and bright vertical lines, and are the spectra of glowing vapours of elements. These spectra serve to identify the elements present in a substance (Spectrum analysis). See Chart 155.
- Specular iron ore a variety of haematite, which see, occurring in rhombohedral crystals, black in colour, and with a metallic splendant lustre.
- Speed of light is approximately 186,000 miles per second in air (300,000 kilometres per second). To find the speed of light in any other medium it is necessary to divide 186,000 by the refractive index of the medium.
- Spessartite, Spessartine the manganese aluminium garnet. See Garnet. The form spessartite has also been used by petrologists for a certain type of rock.
- Sphalerite mineralogical name for zinc blende.
- Sphene R.I. 1-888 --- 1-917 to 1- 914 --- 2-053 S.G. 3-45 to 3-56; H. 5 to 5.5; Monoclinic; Colours, yellow, green, brown and grey; Localities, Switzerland, Mexico and Burma.
- Spherulites (Spherules) Rounded aggregates or rosettes of very fine needle-like crystals radiating from a common centre producing ball-like inclusions which are circles when cut across and polished. An example is orbicular Jasper.
- Spinel R.I. 1-714 to 1-736; S.G. 3-58 to 3-75 (intermediate Mg-Zn type may reach 4-06; H. 8; Cubic; Colours, deep red, rose red and pink, orange-yellow (Rubicelle), purple, blue, grass-green (Chlorospinel), dark green to black (Ceylonite or Pleonaste); S.G. to 3 90; Localities, Ceylon, Siam, Burma, U.S.A.,etc. See Gahnospinel.
- Spodumene R.I. 1-66 --- 1-675 to 1-66 ---1-679; S.G. 3-17 to 3-23; H. 6 to 7; Monoclinic; Colours, yellow, yellowish-green, ice-green, grass-green (Hiddenite) and lilacpink (Kunzite); Localities, U.S.A., Brazil and Madagascar.
- Stag horn see Deer horn.
- Stained chalcedony see Artificial treatment of gemstones, Chart 178.
- Stained jasper see Artificial treatment of gemstones, Chart 178.
- Stalactite a tapered column of mineral matter found pendant from the roof of a cavern and which has been deposited by dripping water.
- Stalagmitic formation a cavern formation the opposite to a stalactite. It may cover the floor of the cavern or may rise as a column from the floor underneath a stalactite. In some cases the two may join to produce a column.
- Star facets the name applied to the eight triangular facets which surround the table in the brilliant cut.
- "Starilian" Trade name for strontium titanate.
- "Starlite" named proposed, in U.S.A., for the blue zircon (heat treated).
- Star stones see Asterias.
- Staurolite R.I. 1-7 --- 1-75 to 1-75 --- 1-76; S.G. 3-4 to 3-8; H. 7 to 7.5; Rhombic; Colour, reddishbrown; Localities, Switzerland and South America. Twinned crystals often in the form of a cross (Cross-stone or Fairystone).
- Steatite (Soapstone) R.I. 1-5 --- 1-59; S.G. 2-6 to 2-8; H. 1. may be higher owing to impurities; Monoclinic; Colours, yellow, brown and reddish. Used for carvings.
- Step cut