ORPIMENT. 



colour, which fuse BB, without imparting 

 any colour to borax, and are malleable after 

 cooling. 



Analysis, by Berzelius : 



Gold 85-98 



Palladium .... 9*85 

 Silver 4-17 



ORTHOCLASE. 



269 



100-00 

 Orpiment. Rhombic: primary form a 

 right rhombic prism with a perfect cleavage 

 parallel to the longer axis. Occurs in small 

 crystals, but rarely ; also massive, foliated, 

 or columnar, disseminated, and sometimes 

 reniform. Colour bright lemon-yellow pass- 

 ing into golden-j'elloAV. Lustre resinous ; 

 pearly on planes of perfect cleavage. Sub- 

 transparent or translucent only at the edges. 

 Sectile. Streak yellow, slightly paler than 

 the colour. Thin laminse obtained by 

 cleavage. Flexible but not elastic. H. l-'5 

 to 2. S.G. 3-4 to 3-48. 



Comp. Tersulphide of arsenic, or As S^ 

 = arsenic 61, sulphur 39 = 100. 

 Analysis, by Laugier : 

 Arsenic .... 61-86 

 Sulphur .... 38-14 



100-00 



BB on charcoal, burns with a bluish 

 flame, and gives off sulphurous and arseni- 

 cal fumes. 



Dissolves in nitro-muriatic acid or am- 

 monia. 



Localities. Taj owa, near Neusohl, in Lower 

 Hungary, in small crystals, in stratified clay 

 and limestone. It is generally found in folia- 

 ted and fibrous masses. Kapnik, in Transyl- 

 vania. Moldawa, in the Bannat. Felso- 

 banya, in Upper Hungary. Hall, in the 

 Tyrol, in Gypsum. St. Gotthard, in Dolo- 

 mite. The Solfatara, near Naples. Jula- 

 merk, in Koordistan. Zimapan, in Mexico. 



The finest specimens of Orpiment are 

 brought from Persia in brilliant yellow 

 masses, with a lamellar texture, called 

 Golden Orpiment. 



Name. Tne word Orpiment is a corrup- 

 tion of the Latin name Auripigmentum, or 

 golden paint (from aurum, gold, and pig- 

 mentum, paint), which was applied to it 

 partly in consequence of its use as a pig- 

 ment, and partly because it was believed 

 to contain a small quantity of gold. The 

 Orpiment employed as a pigment (King's 

 yellow or Orpin) at the present day is pre- 

 pared artificially by subliming arsenious acid 

 with a small quantity of sulphur. It is also 

 used by pyrotechnists and bookbinders, and 



is an active ingredient in a kind of epilatory 

 soap, as well as of a depilatory called 

 Poudre subtile, in combination, according 

 to Dr. Paris, with quicklime and a vegetable 

 powder. Orpiment is the 'Appivizov of the 

 ancients, and 'A^cri^iy,o, of the later Greeks. 

 (Hill.) 



Fig. 315. 



It is distinguished from Native Sulphur 

 by its foliated structure. 



Brit. Mus., Case 12. 



M. P. G. Wall-case 23. 



Orthite, Berzelius. A variety of Allanite, 

 occurring in long, thin, acicular crystals, 

 and massive. Colour blackish -grey, inclin- 

 ing to black. Opaque ; in very thin splin- 

 ters subtranslucent. Lustre vitreous. Streak 

 brownish-gre3\ Brittle. Fracture conchoi- 

 dal, uneven. H. 5 to 5-75. S.G. 3-28 to 3-54. 



Comp. R3Si + ftSi + H. 



Analysis, from Hitteroe, by Rammelsherg ; 



Silica 33-81 



Alumina .... 33-04 



Peroxide of iron . . . g-iQ 



Protoxide of iron . . 8-30 



Protoxide of cerium . , 20-50 



Yttria 1-45 



Lime 9-42 



Magnesia . , . . 0-38 



Potash 0-67 



Water 3-38 



99-11 



BB swells up, boils, and fuses to a black- 

 ish blistered glass; with borax or micro- 

 cosmic salt yields a glass coloured by iron. ■ 



Dissolves in muriatic acid (if not pre- 

 viously ignited), and is converted into a 

 gelatinous mass. 



Localities. Finbo, near Fahlun, in Swe- 

 den, in acicular, diverging prisms, of a dark 

 brown colour, sometimes upwards of a foot 

 long, imbedded in Quartz ; also at Ytterby, 

 in Sweden; Skeppsholra, an island near 

 Stockholm, in black vitreous masses dis- 

 seminated in gneiss; Krageroe, Hitteroe, 

 Arendal, and Fille Fjeld, in Norway; Fin- 

 land; Miask, in the Ural; Dresden, &c. 



Name. From k^'o?, straight. 



Brit. Mus., Case 38. 



Orthoclase, Dana. Orthoklas, Brei- 

 thaupt. Potash Felspar, Oblique: pri- 

 mary form an oblique rhombic prism. Co- 



