290 THE GEOLOGY OP MINNESOTA. 



[Quartzyte. 



Meg. A fine-grained, pinkish quartzyte, composed of quartz, feldspar and a 

 black mineral. It is indistinctly mottled by gray and pink, the gray areas being 

 composed almost entirely of quartz, and the pink areas of quartz imbedded in feld- 

 spar. Along one side of the specimen, and in drusy cavities the minerals of the rock 

 exist in small crystals. The hand sample is sharply divided, into a pink and a 

 dark gray portion. The above description is of the pink portion ; the dark gray part 

 is essentially the same except that the quartz is much decreased in abundance, and 

 there is a corresponding increase of the black mineral. 



Mic. The section, which was made from the pink part of the hand specimen, 

 is composed of quartz &nd feldspar with a little chlorite and green biotitc. The quartz 

 is in sub-angular and more or less rounded grains, and a noticeable feature is the 

 tendency of many of these grains to assume bipyramidal outlines. The outlines, 

 however, are not perfect, but approximate to the perfect bipyramidal form. In some 

 cases these crystals are short and stout, and again they are ragged and irregular, 

 but still show an indication of crystal outlines. This form of the quartz has been 

 noted by Bayley (U. S. Geol. Survey; Bulletin cix), and figured (see figure 12, page 

 86; plate XII, figure a; figure 13, page 93). Some of these imperfect quartz crystals 

 are shown in the accompanying figure. The quartz is also in the form of more or 

 less rounded grains with no indication of crystal planes, and sometimes several of these 

 grains, separated by veins of feldspathic material, are seen to have the same optical 

 orientation. 



FIG. 19. OUTLINES OF IMPERFECT QUARTZ CRYSTALS FROM QUARTZYTE. 

 Crystallographic c in each case is vertical. 



The feldspar is clouded, as in No. 262, and its peculiar feature is that it exists 

 as a cement between the quartz grains. It does not occur in distinct grains, as in No. 

 262, but two or three clear plagioclase grains are seen. The feldspar sometimes 

 extinguishes simultaneously over considerable areas. 



One section. 



Age. Animikie. 



Remarks. This rock, and a number of others from Pigeon point and vicinity, 

 are similar to those described by W. S. Bayley in Bulletin cix, U. S. Geol. Survey, 

 where detailed descriptions, illustrations and analyses are given. u. s. G. 



