366 



THE GEOLOGY OF MINNESOTA. 



[Iron ore and taconyte. 



Age. Animikie. 



Remarks. For a full description and discussion of the taconyte and its granules 

 see Bulletin x. u. s. G. 



No. 440. IRON ORE. 



Perhaps in sec. 11, T. 59-14 W. 



Ref. Annual Report, ix, page 108; Annual Report, xi, pages 156-159. 



Meg. A dark reddish-brown, massive iron ore. Sojne is black and magnetic, 

 other parts are apparently hematite, and much of it gives off water in heating, thus 

 indicating limonite. 



No section. 



Age. Animikie. u. s. G. 



No. 441. IRON ORE AND TACONYTE. 



Same place as No. 440. Near the top of the shaft. 



Ref. Annual Report, viii, pages 150, 151; Annual Report, ix, page 109. 



Meg. The ore is banded and irregularly spotted with gray, the latter being 

 siliceous and somewhat globular, characteristic of taconyte. 



Mic. The section shows the characteristic round silica grains stained with 

 magnetite, and in other parts is wholly occupied by iron ore. 



The following sketch shows the manner of distribution of the ore in a section 

 of this rock which is more siliceous than the average. There are several characters 

 to be noted : 





* j 



.;' X^*y*U*< 



FIG. 20. DISTRIBUTION OP CLUSTERS OF 

 MAGNETITE GRAINS IN THE PERIPH- 

 ERIES OF SILICEOUS BALLS. 



FIG. 21. SHAPES OF THE MAGNETITE CLUSTERS 

 SEEN IN FIGURE 20. 



These are chosen from a great number that generally show no grouping into cellular arrangement. 



1. The ore consists of a very h'ne powder or dust, which is black in the section examined as if it were 

 magnetite, and, except for the manner of grouping, which seems to have depended on some earlier or perhaps 

 cotemporary cause, this fine powder is the idiomorphic or first element that shows independent or original char- 

 acters. These dust-like particles are prevailingly in clusters, somewhat as roughly shown in the figure (figure 

 20), except that each little cluster comprises many times as many of the particles as are shown in the figure. 



2. These clusters are again grouped, in a larger way, into balls or siliceous grains, and in these larger 

 grains they are most numerous at the peripheries. There is, besides, a thread of dust-like opaque particles at 

 the very periphery of each of these balls, making thus a dark thread which quite distinctly outlines each section 

 of a ball. 



