CLINTON OOLITIC IRON ORE 769 



Clinton ores of the Southern States, as is clearly indicated by the follow- 

 ing statements. In describing the Clinton ores of the Birmingham dis- 

 trict, Burchard says : ''One of the two varieties of ore generally predomi- 

 nates in a bed, but in certain localities the fossil and oolitic materials are 

 mixed in nearly equal proportions." *° McCallie in describing the ores 

 from Georgia says: "In some of the beds these particles make up the 

 greater part of the ore, while in other beds they are almost entirely 

 wanting.^' *^ 



As the writer's field, experience with these Clinton ores has been rather 

 limited, the following description is based largely on thin sections and 

 the published reports of those who have made a special study of this 

 subject. 



The Clinton oolites possess a concentric structure which is not always 

 apparent in thin section under the microscope, but which can be readily 

 seen if the individual spherules are separated from the matrix and tapped 

 with a light hammer. Each spherule will break into a series of concen- 

 tric shells. The material is so opaque that this concentric structure can 

 not be seen under the microscope, but the nature of the nucleus is readily 

 made out. This nucleus usually consists of a well rounded quartz sand 

 grain, but it may be a fragment of a shell. According to McCallie, some 

 of the spherules may have a central nucleus of oxide of iron surrounded 

 by a layer of calcite or silica, which in turn may be inclosed in layers of 

 oxide of iron. He furthermore reports that in nearly every section of 

 these oolites from Georgia spherules can be found with a nucleus of a 

 granular, green, or yellowish green mineral. In some cases this green 

 mineral occurs as- granules within the spherule even when they do not 

 form the nucleus. 



When the spherules are treated with hydrochloric acid, the iron oxide 

 is dissolved out and there remains a skeleton of silica with a spongy and 

 porous texture. This silica is often arranged in concentric layers which 

 can be peeled off like the layers of an onion. This silica is amorphous.*^ 



These oolites of iron ore are very frequently ^associated with fragments 

 of fossils which have been more or less completely replaced by the iron 

 oxide. When these are treated with hydrochloric acid, they, too, leave 

 behind a skeleton of silica, although this material can not be seen in 

 microscopic sections.*^ 



This description is sufficient to indicate that the Clinton iron ore is 

 made up in part of true oolites with concentric structure and generally 



«>Bull. 400, U. S. Geological Survey, p. 26. 

 *iBull. 17, Geol. Survey Georgia, p. 168. 

 *2 McCallie: Loc. cit, pp. 173-174. 

 " Smyth : Loc. cit., p. 489. 



