CHAPTER XIY. 



THE LESSER METALS: ALUMINIUM, ANTIMONY, ARSENIC, 

 BISMUTH, CHROMIUM, MANGANESE. 



ALUMINIUM. 



2.14.01. The importance of aluminium grows with improved 

 and cheaper methods of production. Its sources have been alums, 

 either natural or artificial, corundum, cryolite, and bauxite. The 

 first of these is formed in nature by the decay of pyrite in shales 

 and slates, and is little, if at all, used at present. The second is 

 now more valuable as an abrasive. Cryolite (Al 2 F 6 .6NaF), a pe- 

 culiar mineral, occurring in quantity only in Greenland, has been 

 most largely employed until the recent discoveries of bauxite have 

 made it less necessary. The cryolite forms an immense bed or vein 

 in gneiss at Evigtok, on the Arksut Fjord, Greenland. 1 Bauxite 

 (A1 2 O 3 .3H 2 O) has long been valuable as a refractory material, but 

 at present it is also used as a source of aluminium. Bauxite occurs 

 in quantity in several of the Southern States. In Floyd County, 

 Georgia, it covers about half an acre. Near Little Rock, Ark., 

 it is in greatest quantity, and forms an interbedded mass in fer- 

 ruginous Tertiary sandstone. Small amounts of oxide of iron 

 partially replace the alumina at times, but the average grade is 

 better than the foreign. It is considered by J. F. Williams as 

 probably a hot-spring deposit, but the origin is obscure. Dis- 

 covered deposits aggregate over a square mile and range up to 40 

 feet thick. 2 



1 G. Hagermann, " On Some Minerals associated with the Cryolite in 

 Greenland," Amer. Jour. Sci. , ii. , XLII. 93. J. W. Taylor, " On the Cryolite 

 of Evigtok, Greenland," Quar. Jour. Geol. Sci., XII. 140. 



2 J. C. Branner, "Bauxite in Arkansas," Amer. GeoL, Vol. VII., p. 

 131, 1891. Ann. Rep. GeoL Survey Arkansas, 1888, Vol. I. J. F. Will- 

 iams, Ann. Rep. Geol. Survey Arkansas, 1880, Vol. II., p. 124. E. Nichols, 

 " An Aluminium Ore, Bauxite," M. E., XVI. 905. 



