COLLECTIONS IN KCONOMIC GKOLOOY AND MKTALM'KCV, 171 



can bi* utilized for bleaching in a variety of ways. Tlic aiiiKimt of 

 chlorine ;,Mveii otF depends upon the anionnt of binoxide of inanj^anese 

 (MnO.) in the ore, and this determines the valne(»f thcor*'. Orescrontain- 

 in^ less than 7(> per cent, of binoxide of inanjianes*"! have little <»r no 

 value. In steel-making' the ores are smelted, either alone or mixed 

 with iron ores, in a shaft furna«;e, just as iron ores ar«' smtltril. Tdr 

 this |>urpose the ores must <'onlain only a very small amount of j»hos- 

 phorus. The protluct is known as spiej;eleisen or ferroman;;anese, 

 according to the amount of manganese it contains. It contains a larger 

 amount of combined carbon, and is used in the steel piocesses to give 

 carMdu to the metal. It also improves the i)hysical properties of the 

 metal by introducing a little manganese, which aids especially in pro- 

 ducing sound eastings. Specimens of spiegeleisen and ferromanganese 

 will l)e found in the steel collections. 



ISesides the manganese ores in the Census series of iron ores, liie fol- 

 lowing characteristic specimens are shown: 



(1) Crystallized and ueissivf. Tloyd County, Georgia. (563.54.) 



(2) Crystallized and massive. Chninney Hill, IJartow County, Georj^ia. (."tGIUD.) 



(3) Massive. Dohbius Mine, Bartow County, (Jeorgia. (r)(;34-4.) 



(4) Massive. Indepeudeuce Couuty. Arkansas. (,5(5401.) 



NICKEL A N D C O H A L T. 

 Nickel Mineral. 



:\nLLERITE. 



Composition: NiS. Sidphide of nickel, containing nickel Gaper cent, 

 and sulphur ."{.j j)er cent. 



It crystallizes in the ihond)ohedral .system, crystals usually very 

 much elonjiated. It also occurs in radiated and columnar coatings. It 

 varies in hardness fr(>m A to -'i.-j, and in s[)eci(ic gravity from 4.(> to ~)Ai, 

 has a full metallicluster an<l brass yellow color, with often a gray ii ides- 

 cent tarnish. Millerite is an im])ortant nickel mineral, but is seldom 

 foMUtl pure in large amounts. 



To illustrate the occurrence of millerite the following specimen is 



shown here. Other specimens are includetl in the ore series: 



I) Thin, lilirousettating on deconipose«l roek. (iai>Mine, Lailcas(<'r County, Penn- 

 sylvania. (»)5:5(»7.) 



Cobalt and Nkket, Mineral, 

 linn.kite. 



Coniposition : L'CoS-f CoS^. Sulphideof cobalt, <-ontaiiiing cobalt 5.S 

 per cent, and sul|)liur IL' per cent. The cobalt is always replaced by 

 more or less nickel, and gi'uerally al.so i)y <'opper. 



It crystallizes in the isometric sy.stem in cubes and octalicdrmis and 



