1004 THE GEOLOGY OP MINNESOTA. 



[Oranite. 



which warrants the following proportionate distribution of the minerals: 



Biotite, specific gravity 2.8 to 3.2, 12 per cent. 



Muscovite(?), " 2.75 to 3.2, 



Above 3., 9-29 



Hornblende, specific gravity 3.2 to 3.3, 



Epidote, 



Zoisite(?), 



Apatite, 



Sphene, 



Tourmaline, 



Pyrite, 



3.25 to 3.36, 

 3.25 to 3.36, 

 3.16 to 3.22, 

 3.3 to 3.7, 

 3. to 3.24, 

 4.9 to 5.2, 



3. to 2.661, 34.66 



Calcite(?), specific gravity 2.72, 



2.661 to 2.642, 25.02 



Andesine-Oligoclase, spec, gravity 2.645, 

 Quartz, 2.65, 



2.642 to 2.58, 7.60 



Below 2.58, 11.43 



Orthoclase, specific gravity 2.54 to 2.56, 



Microcline, 2.56, 



Kaolin, 2.34 to 2.57, 



100.00 per cent. 



Hence, basing a calculation on the fairly accurate determination of the biotite, 

 the minerals are approximately in the following proportions: 



Orthoclase, 18.00 



Andesine-Oligoclase, 16.00 



Biotite, 12.00 



Microcline, 12.00 



Quartz, 12.00 



Hornblende, 10.00 



Epidote, 7.00 



Kaolin, 5.00 

 Apatite, 



Zoisite, . - 3.00 



Sphene, 2.00 



Tourmaline, pyrite, calcite and muscovite, 1.00 



100.00 



The anomalous mineral figured by the author of the foregoing description 

 appears to be a twinned hornblende with two central remnants of pyroxene. The 

 hornblendic zones, surrounding the nuclei of pyroxene, embrace micro-poikilitically 

 several grains of quartz oriented uniformly with the adjacent quartzes, but no 

 inclusions are in the pyroxenic cores, except that about their margins hornblendic 

 spurs crowd upon their boundaries. The hornblende seems to have been formed from 

 two original augites whose cleavage and orientation do not agree either with each 

 other or with the surrounding hornblende. 



The confused aggregates above called kaolin are more likely to be of the nature 

 of rejected but recrystallized substances embraced in the regenerated feldspars after 

 complete metamorphism, consisting partly of mica and in part probably of fine- 

 grained epidote. There is nothing in the rock that can be correctly attributed to 

 decay since its final consolidation. Three sections. 



Age. Archean. N. H. w. 



