908 THE GEOLOGY OP MINNESOTA. 



(Taconyte. (iabbro. 



Mic. The section shows a granular aggregate of feldspar, pinkish diallage and 

 olivine. The latter is altering to a fibrous green material, and throughout the section 

 is much of a very fine-grained, secondary mineral, which appears to be calcite. The 

 feldspar is frequently, though not always, polysynthetically twinned; equal extinc- 

 tion angles in sections cut normal to 010 run up to 20, indicating a plagioclase as 

 basic as andesine. A little biotite is present, as is also a small amount of magnetite. 

 Three sections. 



Chemical analysis. An analysis of this rock gave the following result: 



SiO 2 Al.O, Pe 2 O 3 FeO CaO MgO MnO Na 2 O K 2 O CO 2 H 2 O Total 

 49.07 17/21 .46 12.18 9.66 3.60 trace 2.96 trace 2.70 1.55 99.39 



Age. Cabotian. 



Remark. This is one of the rocks to which the name " muscovadyte " has been 

 applied. u. s. G. 



No. 879G. TACONYTE (?) 



E. % S. W. ^ sec. 21, T. 65-4 W., north of the works of the Gunflint Lake Iron company. 

 Ref. Annual Report, xxi, page 67. (Compare No. 1896.) 



Meg. A fine-grained, heavy, banded rock, the bands being composed of (1) 

 Magnetite, and (2) Very fine-grained, gray, siliceous material. 



Mic. With a scattered taconitic structure, evinced both by the prevalence of 

 an interlocking quartz background and by globular aggregations of siliceous iron 

 ore, this rock shows much pyroxene, which serves to include poikilitically many fine 

 granules of magnetite, of quartz and of globular pyroxene. There are also a few 

 needles of actinolite that radiate into the quartz from some of the small augite grains, 

 and a small amount of cummingtonite. Two sections. 



Age. Animikie(?) 



Remark. The irony, taconitic globules of this rock are like those of the Mesabi 

 iron re; but here they are mingled with much pyroxene, some of which is in imper- 

 fect crystals as large as the taconitic globules. The usual quartz mosaic serves as 

 background for both these substances. This pyroxene is an anomaly for taconyte. 

 The taconitic nature of this rock is determined by the patchy and globular grouping 

 of the magnetite grains, these grains being sometimes quite coarse, but also sometimes 

 finer, and more scarce or wanting in some portions of the slide. N. H. w. 



No. 989G. GABBRO (with diallage). 



S. W. % N. W. J sec. 11, T. 64-3. At the south end of the portage from Tucker lake to the long lake 

 next south. 



Ref. Annual Report, xxii, page 84 ; Final Report, vol. iv, page 489. 



Mi'<j. Granulitic gabbro, heavy with magnetite. 



Mic. The minerals are fresh and all have rounded outlines, as if they were 

 formed simultaneously. The augite is uniformly diallagic, and, while it spreads irreg- 



