REDISTRIBUTION OF MANGANESE. 989 



Other iron-bearing minerals also are formed. Among them garnet and 

 staurolite are important; but various other heavy iron-bearing silicates 

 develop, among which may be mentioned ilmenite, humite, clinohumite, 

 ottrelite. and chloritoid. 



MANGANESE. 



According to Clarke's estimate of 1891 manganese forms 0.07 per cent 

 of the outer 1 miles of the crust of the earth, including the lithosphere, 

 hydrosphere, and atmosphere. In the lithosphere alone the amount 

 estimated is 0.08 per cent. In his estimate of 1900 he reduces this amount 

 to 0.07 per cent." By this estimate manganese is thirteenth in the scale of 

 abundance. If these amounts of 0.08 and 0.07 per cent were reckoned as 

 Mn0 3 they would be respectively 0.1265 and 0.1107 per cent. 



Very small percentages of manganese are reported in the following 

 silicates: lavenite, arfvedsonite, spessartite, piedmontite, and astro phyllite. 

 The amount in no case is large enough to make the element an essential one. 

 Mang-anese is reported among the subordinate constituents of the meteorites. 

 A trace of it is reported in the shales and sandstones, and in 843 limestones 

 manganese oxide composes 0.04 per cent of the rock. Since the mass of the 

 limestones is so small as compared with the shales and sandstones, manganese 

 in the limestones is trivial compared with that which is present in the 

 original rocks. The probable explanation of the deficiency of manganese in 

 the common secondary rocks is that the manganese is segregated in 

 manganese ore deposits precisely as the iron, the reactions for segregation 

 being analogous throughout. (See pp. 1198-1199.) Thus the manganese 

 reported in the sedimentary rocks is found in limestones — -that is, in car- 

 bonate rocks. Iron is, in a similar manner, to a large extent segregated 

 in connection with carbonate deposits. 



The relative masses of the segregated manganese ore and iron ore 

 are interesting, since these two compounds go through analogous trans- 

 formations, producing ore bodies under similar conditions, and in very 

 numerous cases being associated in the same ore deposits. But subject to 

 the law of mass action the abundant element iron produces ore deposits of 

 enormously greater size than does the rarer element manganese. The 

 amounts of iron and manganese in the original rocks are 4.64 and 0.07 

 per cent respectively. Thus if the two elements were segregated in the 



a Clarke, tit., Bull. 78, p. 39; Bull. 168, p. 15. 



