8 JET 



}v-frctly transparent, and is either colourless or grey, with tinges of green, blue, red, 

 and yellow of various shades, but generally smoky and ill-defined. It occurs in worn 

 angular pieces, or in small detached crystals, rarely exceeding 6 or 8 carats in weight, 

 chiefly in the sand of a river in Ceylon. The surfaces of the crystals are smooth, and 

 possess a lustre more nearly approaching that of the diamond than any other gem. 

 At the present day, though out of fashion and in no request, it is still occasionally 

 sold for inferior diamonds. 



Davy says that the light grey varieties of the zircon are sold by the inhabitants of 

 Ceylon as imperfect diamonds, the natives being altogether ignorant of the true 

 nature of the mineral. It is most abundant in the district of Matura, whence it has 

 its common name in Ceylon of Matura diamond. The colourless zircon is also cut 

 and sold as a false diamond in the bazaars of India. H.W.B. 



JAROSITE. A hydrous sulphate of peroxide of iron, with an alkaline sulphate. 

 It takes its name from Barranco Jaroso, in the Sierra Almagrera, in Spain. 



JASPER (Jaspe calcedoine, Fr. ; Jaspis, Ger.) is a sub-species of quartz, of which 

 there are five varieties: 1. The Egyptian red and brown, forming nodules with 

 ring or tendril-shaped delineations. 2. Porcelain jasper, or clay altered by heat, 

 and differing from true jasper by being fusible on the edges, before the blowpipe. 

 3. Striped or riband jasper. 4. Common jasper. 5. Agate jasper. The prettiest 

 specimens are cut for seals, and for the inferior kinds of jewellery ornaments. See 

 LAPIDAHY. H.W.B. 



JATROPHA 1YXANIHOT. A plant belonging to the Euphorbiacete, from which 

 the Cassava meal is prepared, and from the expressed juice of which are obtained 

 Cassava starch and Tapioca. See TAPIOCA. 



The seeds of Jatropha purgans yield jatropha oil, and the nuts of this and some 

 other species of Jatropha are known as ' Physic nuts.' 



JEAN. A twilled cotton, usually stripped. Satin-jeans are woven so as to present 

 a smooth glossy appearance. It is used for stays, &c. 



JELLY, ANIMAL. See GELATINE ; GLUE ; and ISINGLASS. 

 JELLY, VEGETABLE. A great many vegetable productions yield upon Infusion 

 or decoction gelatinous solutions. These vary very much in character. The jelly of 

 ripe currants and other berries is a compound of mucilage and acid, which loses its 

 power of gelatinising by prolonged ebullition. 



JEMMIES. A woollen cloth made in Scotland. 



JERKED BEEF. Beef dried in the sun : much of this has been introduced from 

 the South American States, but it has not hitherto been much used, although sold at a 

 very low price. 



JERUSALEM ARTICHOKE. The edible tubers of the Helianthus tuberosus. 

 The epithet of ' Jerusalem ' is a corruption of the Italian girasol. 



JESSAMINE or JASMINE. A well-known family of plants. The Jasmium 

 fruticans, a native of the southern parts of France, J. odoratissimym, a native of India, 

 and J. sumbac, a native of India and Arabia, are used to obtain the essential oil or 

 jasmine. See PEEFTJMEBT. 



JET. (Jaiet, mjais, Fr.) Jet occurs in the upper lias shale in the neighbour- 

 hood of Whitby, in Yorkshire, in which locality this beautiful substance has been 

 worked for many hundred years. The jet-miner searches with great care the slaty 

 rocks, and finding the jet spread out, often in extreme thinness between the lamina- 

 tions of the rock, he follows it with great care, and frequently he is rewarded by its 

 thickening out to two or three inches. 



The best jet is obtained from a lower bed of the upper lias formations. This bed 

 has an average thickness of about 20 feet, and is known as jet rock. An inferior 

 kind, known as joft jet, is obtained from the upper part of the upper lias, and from the 

 sandstone and shale above it. The production of jet in this country appears to be 

 limited to the coast of Yorkshire, from about nine miles south of Whitby to Boulby, and 

 about the same distance to the north ; the estates of Lord Mulgrave being especially 

 productive. There is a curious allusion to this in Drayton's ' Polyolbion ' : 



The rocks by Monltgrave, too, my glories forth to set, 

 Out of their crannied rocks can give yon perfect jet. 



l)r. Young, in his ' Geology of the Yorkshire Coast,' writes ' Jet, which occurs here 

 in considerable quantities in the aluminous bed, may be properly classed with fossil 

 wood, as it appears to be wood in a high state of bitumenisation. Pieces of wood im- 

 pregnated with silex are often found completely crusted with a coat of jet about an 

 inch thick. But the most common form in which the jet occurs is in compact masses 

 of from half an inch to 2 inches thick, from 3 to 18 inches broad, and of 10 or 12 feet 

 long. The outer surface is always marked with longitudinal striae, like the grain of 



