144 PHYSIOGRAPHY. CLASS II. 



als. Often strongly connected. Faces of compo- 

 sition rough. 



OBSERVATIONS. 



1. According to STROMEYER, the prismatic Lead-baryte 

 consists of 



Oxide of Lead 72-47. 



Sulphuric Acid 26-09. 



Water 0-12. 



Hydrous Oxide of Iron 0-09. 



Oxide of Manganese 0-06. 



Silica, &c. 0-51. 



Its composition, when pure, is expressed by Pb S 2 , or 73-56 

 oxide of lead and 26-44 sulphuric acid. It decrepitates in 

 the flame of a candle, and frequently assumes a slight red- 

 dish tinge on the surface. Reduced to powder, it melts 

 easily before the blowpipe into a white slag, which is re- 

 duced to metallic lead by the addition of soda. 



2. It is found in lead and copper veins traversing clay 

 slate and greywacke slate, particularly in the upper parts, 

 along with various ores of lead and copper, also with pris- 

 matic Hal-baryte, prismatic I ron-ore, rhombohedral Quartz, 

 and other species. 



3. Prismatic Lead-baryte is found at Leadhills and "Wan- 

 lockhead in Scotland, Parys mine in Anglesea, Mellano- 

 weth in Cornwall ; also at Clausthal and Zellerfeld in the 

 Hartz, near Freiberg in Saxony, in Baden, in the mining 

 district of Siegen in Prussia, in Spain, Siberia, and the 

 United States of North America. 



6. AXOTOMOUS LEAD-BAEYTE. 



Plomb carbonate rhomboidal. BOURNON". Cat. p. 343. 

 Sulphato-tri-Carbonate of Lead. BROOKE. Edinb. Phil. 

 Journ. Vol. III. p. 118. HAIDINGER. Trans. Roy. 

 Soc. Edin. Vol. X. p. 217- 



Fundamental form. Scalene four-sided pyramid. 



