GARNET 535 



Gamboge is employed as an artist's colour ; it is used to colour varnishes and 

 lacquers, and it is administered medicinally. 



Our imports of gamboge were in 1863, 388 cwts., value 3.268Z. ; in 1864, 42 cwts., 

 value 5201. ; they have not been reported of late years. 



GAMMAM. A dye-stuff, so called, from Tunis. Examples were sent to this 

 country in 1851, but it does not appear to have been introduced since that time. 



GANGCTB. A word derived from the German Gang, a vein or channel. It 

 signifies the mineral substance which either encloses or usually accompanies any 

 metallic ore in the vein. Quartz, carbonate of lime, sulphate of baryta, sulphate of 

 lime, and fluoride of calcium, generally form the gangues ; but a great many other 

 substances become such when they predominate in a vein. In mineral works the 

 first thing is to break the mixed ore into small pieces, in order to separate the 

 valuable from the useless parts, by processes called stamping, picking, sorting. 

 Literally, Gang is a course or passage. See MINING. 



GAiraTSTER. The name of a bed of highly siliceous fire-clay. It is usually 

 extremely hard, and contains many Stigmaria roots. It is found beneath some of the 

 seams of coal in Lancashire and other places. The gannister when crushed and, if 

 necessary, mixed with a little more plastic clay, produces a brick of the most re- 

 fractory description. It is also used for lining the Bessemer converters, and similar 

 purposes. 



GARANCEUX. See MADDER. 



GARAXrciltT. See MADDER. 



GARLIC. Allium satiwm. This plant is well known, and is much used in 

 flavouring sauces. 



It is found by analysis to contain an acrid volatile oil, gum, woody fibre, albumen, 

 water, with sulphur, starch, and saccharine matter. The oil of garlic is a sulphide of 

 allyle, A11S = COTS. [(C 3 H 5 ) 2 S.] 



GARNET. (Grenat, Fr. ; Granat, Gear.). Garnet is a double silicate of cer- 

 tain bases, such as alumina, lime, magnesia, oxide of iron, &c. 



There are six sub-species of garnet, viz. : 



I. Alumina-lime garnet, consisting of the silicates of alumina and lime. 



II. Alumina-magnesia garnet, consisting of the silicates of alumina and magnesia. 



III. Alumina-iron garnet, consisting of the silicates of alumina and iron. 



IV. Alumina-manganese garnet, consisting of the silicates of alumina and man- 

 ganese. 



V. Iron-lime garnet, consisting of the silicates of iron and lime. 



VI. Lime-ohrome garnet, consisting of the silicates of lime and oxide of chromium. 



I. Lime-garnet, or grossular, is composed of silica, 40-1 ; alumina, 227 ; lime, 37*2 

 = 100-0. Colour, pale greenish, clear red, and reddish orange, cinnamon colour. 

 Before the blowpipe, fuses to a slightly greenish glass or enamel ; soluble, when pow- 

 dered, in concentrated muriatic acid. 



This section comprises cinnamon-stone or Essonite, grossular or Wiluite, Boman- 

 zovite, topazolite, and succinite. 



II. Magnesia-garnet is of a deep coal-black colour, with a resinous lustre. The 

 variety from Arendal is composed of silica, 42-45 ; alumina, 22-47 ; protoxide of iron, 

 9-29 ; protoxide of manganese, 6'27 ; magnesia, 13-43 ; lime, 6*53 ; = 100-44. (Wdcht- 

 meister.) Before the blowpipe, easily fusible, forming with intumescence a dark 

 greyish-green globule, which is non-magnetic. 



III. Iron-garnet comprises the almandine or precious garnet, allochroite, and com- 

 mon garnet. It is composed of silica, 36-3 ; alumina, 20*5 ; protoxide of iron, 43'2 = 

 100-0. Before the blowpipe, fuses rather easily with an iron reaction. 



IV. Manganese-garnet, or spessartine, is of a brownish-red colour, and is composed 

 of silica, 35-83; alumina, 18'06; protoxide of iron, 14-93; protoxide of manganese, 

 30-96 = 99-78. (Analysis of M. garnet from Haddam, U.S., by Seylert.) Before the 

 blowpipe, gives a manganese reaction. 



V. Iron-lime garnet includes aplome, colophonite, melanite, and pyreneite. These 

 vary in colour from dark red, brownish-black, to black, and possess a shining lustre, 

 which is sometimes resinous, as in colophonite. 



Analysis of the aplome of Altenau : Silica, 35*64 ; lime,' 29-22 ; protoxide of iron, 

 30-00; protoxide of manganese, 3'01; potash, 2-35 = 100-22. Wachtmeister. 



VI. Lime-chrome garnet, or ouvarovite, is of an emerald-green colour. Sp. gr., 

 3*418. Before the blowpipe it is infusible alone, but with borax affords a chrome- 

 green glass. It occurs at Bissersk, in Russia. 



Analysis by Erdmann : Silica, 36'93 ; alumina, 5'68; peroxide of iron, 1-96; oxide 

 of chrome, 21-84; magnesia, 1-54 ; carbonate of lime, 31-66; oxide of copper, a trace, 

 = 99-58. 



The garnet varies greatly in transparency, fracture, and colour j but when the 



