SULPHIDES, ARSENIDES, ANTIMONIDES 



FIG. 400. Cinnabar Twins. Hu-Nan, China. 



from Mount Avala, Servia. Beautiful examples of penetrating 

 rhombohedral twins often repeated are obtained in the province of 

 K \\virho\v, China. Twin- 

 nil ig lamella parallel to 

 the base show Airy's 

 spirals as in quartz. The 

 rotary polarization is very 

 strong, some fifteen times 

 that of quartz in sections 

 of the same thickness, 

 while the index of refrac- 

 tion is the highest of min- 

 erals. 



Mercuric sulphide is 

 dimorphous; the red cin- 

 nabar forms at a tempera- 

 ture above 45, while the black isometric, tetrahedral form, meta- 

 cinnabar, forms below 45 C. ; the latter form was formerly 

 plentiful at the Reddington mine, Lake County, California. 



Cinnabar is associated more abundantly with sedimentary de- 

 posits, shales, slates, and organic matter than with quartz schists 

 or porphyries. 



The concentrations of cinnabar, forming impregnations in lime- 

 stones and sandstones, or filling fissures, cracks, and cavities in 

 sedimentary formations near regions of igneous action, owe their 

 origin in most cases to ascending hot alkaline solutions carrying 

 mercury sulphide, as in case of the Steamboat Springs, Nevada ; 

 from such solutions the cinnabar is either precipitated by dilution 

 of the solution, by a reduction of pressure, or by contact with or- 

 ganic matter. Pyrite, marcasite, sulphur, barite, gypsum, cal- 

 cite and quartz are the usual associates. 



Cinnabar is the principal ore of mercury ; the largest producing 

 deposits are Idria, Austria, and Almaden, Spain. In the United 

 States cinnabar is mined in California at New Idria and New Alma- 

 den ; in southern Nevada, and at Terlingua, Texas. 



The artificial product is used as vermilion paint and is manu- 

 factured on a large scale by distilling in iron retorts a mixture of 

 8 parts sulphur and 42 parts mercury. In the wet way cinnabar 

 may be produced by dissolving a mixture of mercury and sulphur 

 in a caustic potash solution and heating above 45 C., as below this 

 temperature the black phase will form. 



