MINERALOGY. 



conf.derably from the analyfis of Gerliard, which ive have 

 given, and are, 



Silex - - - - 36-75: 



Alumine - - - " 34'50 



Magnefia - - - " °-'5 



Oxyd of iron with a trace of (^ ^i 

 manganefe - - - ) 



According to Gerhard, 



Silex - - - - 



Alumine - - - - 



Magnefia - - - - 

 Oxyd of iron with a trace of) 

 manganefe - - - j 



92.50 



36.50 

 31.0 

 1.25 



23.50 



92.25 



The cq'ftals of fchorl are longitudinally ftreaked, and 

 have externally a (hining liillre. It occurs in the granite 

 rocks of Cornwall, and intermixed with quartz, when it 

 forms a compound rock, known to Cornifli miners by the 

 name of cocile. Very magnificent cryftals of fchorl have 

 recently been difcovered near Bovey Heathfield, in Dcvon- 

 fhire. See Tourmaline. 



Schiller-Spar, Diallage metalloule, Haiiy, occurs 

 moft frequently in laminx difleminated in ferpentine, and 

 is reo-arded by fome mineralogifts as cryftallized ferpentine. 

 The colours are, ohve-green, pinchbeck-brown, and yel- 

 lowifli-brown. The luftre of the principal frafture is 

 fplendent and pfeudo-metallic ; the crofs fracture is dull 

 and ghmmering. The cleavage is diftinft in the diretlion 

 of the laminae. According to Bournon, the primitive 

 form is a reftangular four-fided prifm, in which the bafes 

 are fet on the broadell lateral planes, forming with them 

 angles of 85° and 95°. The prifm is divifible both in the 

 direftion of the lateral and terminal planes, but moft eafily 

 parallel with the latter. Schiller-fpar is tranflucent in thin 

 laminas ; it yields a greenilh-grey itreak, is fettile, and 

 fofter than hornblende. 



SciiORLACEOUS Beryl. See Pycmite. 



Selenite, or Cryjlalli^ed Gypfum, See Gypsum. 



Serpentite, Noble and Common. See Serpentine. 



Shale, Coal-Shale and Bituminous Shale, a name given 

 to the argillaceous ftrata which accompany coal. Thefe 

 confift of clay more or lefs indurated and flaty, and inter- 

 iriixed with a portion of carbonaceous or bituminous matter. 



Siberite, a name given by fome mineralogifts to 

 Rubelike; which fee. 



Silver-ores. (See Silver.) A fpecies of native 

 filver occurs in Norway, which contains 28 parts in the 

 100 of gold, and is called auriferous native Jiher. On ac- 

 count of the gold, its fpecific gravity is greater than native 

 fdver. Its other charafters, except the colour, (which 

 inchnes to brafs-yellow,) agree with native filver ; which 

 fee, under Silver-Ores. 



An ore of filver containing bifmuth has been found in 

 one mine on the Schapbach, in the Black Forell. It is 

 called bifmuthic filver. It is a pale lead-grey, is foft, feftile, 

 and eafily frangible. Before the blow-pipe metallic glo- 

 bules oo/.e out, which, on the addition of borax, unite in 

 one metallic button, which is brittle, and of a tin-white colour. 

 It contains 27 parts of lead, 33 of bifmuth, and 15 of ful- 



phur, combined with a portion of iron and fulphur, and one 

 part copper. 



Corneous Silver-Ore, or Horn Silver, is divided by Mr» 

 .Tamefon, in the laft edition of his Mineralogy, into four 

 fub-fpecies ; conchoidal, radiated, common, and earthy corneous 

 filver-ore. 



Conchoidal corneous Silver-Ore. — Its colours are greyidi. 

 or greenifti-white. It occurs maffive in compaft hme-ftone, 

 at Guantahoygo in Peru ; it has an adamantine luftre, and 

 is the purell kind of corneous filver known, containing 



Silver - - - - 76 



Oxygen .... ^.5 



Muriatic acid ... 16.^ 



The radiated corneous Silver-Ore has a dark -green colour, 

 and, like the preceding, has hitherto been found only in 

 South America. 



Common corneous Silver-Ore, (fee Silver-Ores,) has 

 been found in fome of the mines in Cornwall, particulai-ly 

 at Huel-Mexico, and in a mine near Peranzabula, on the 

 north-eaft of Cornwall. In the analyfis of this ore, we have 

 ftated the conftituent parts at 68 of filver, and 28 of muriatic 

 acid ; but 6 parts of the latter are oxygen. 



Earthy corneous Silver-Ore is very fort, and almoft friable. 

 This mineral is an intermixture of corneous filver-ore and 

 alumine. 



Earthy Silver-Glance Vip-pezrs to be a decompofingfidphuret 

 of filver. It has a blueifti-black colour, and varies from 

 friable to folid ; it is dull or glimmering, but yields a. 

 metallic ftreak ; it occurs with other ores of filver in veins. 



Under the localities of filver in England, in the article 

 Silver-Ores, for Benalften r. Beeralften, Devonfhire. One 

 of the richeft repofitories of filver is the Weal Duchy Mine, on 

 the banks of the Tamar, above Plymouth. Silver-ores occur 

 there in regidar veins, but are alfo difleminated in nodules, 

 through the rock itfelf, which is killas or clay-flate. The 

 ores are, native capillary filver in confiderable branches, 

 vitreous filver-ore, black filver, and ruby filver-ore. Under 

 the article Silver, we have given the annual quantity of 

 gold and filver obtained in Europe, South America, and 

 part of Afia, as given by Humboldt, in killogrammes, which 

 reduced to the value of the pound fterhng is as under : 



Gold. Silver. 



Europe - - 178,697 468,177 



Northern Afia 74>iZ4 192,966 



America - - 2,382,315 7,071,830 



£2,635,136 7>732.973 



Total annual value 10,368,109/. ; a fum not equal to the 

 payment of one-half of the intereft of the national debt of 

 Great Britain ! 



Slate, or Slate-Clay, Werner. See Slate. 



Slate-spar, Chaux carbonatee nacre, Yr. (See Slate- 

 Spar.) Though this is made a diftinft fpecies of the lime- 

 ftone family by fome mineralogifts, it is compofed of car- 

 bonate of lime with an admixture of about three or four 

 parts in the hundred of manganefe or iron with water, to 

 which probably its nacry luftre may be owing. It occurs in 

 fome parts of Cornwall, and in Scotland. 



Slikensides, a name given by the Derbyfliire miners to 

 galena or lead-glance, when it forms a fmooth pohfiied fur- 

 face or lining to veins. 



Smaragdite, green diallage ; Diallage verte, Haiiy. See 

 Diallage. 



Soap-Stone, a variety of fteatite, is found in Cornwall, 



and 



