ISO 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



rather abundant and a very few minute grains of quartz, small prisms of 

 apatite, and a few crystals of pyrite can be recognized. Numerous dark 

 brown to black streaks arranged parallel to the cleavage represent carbon- 

 aceous matter. There is a system of parallel veinlets less than a millimeter 

 across, which are normal to the slaty cleavage ; fractures through the centers 

 of these veins show small grains of calcite and blotches of cupriferous 

 pyrite. The surfaces of a system of later fractures are irregular and are 

 coated with carbonates. Sections of the veinlets mentioned are made up in 

 large part of an isotropic mineral which is nearly colorless in the thin section. 

 In the hand specimen it is pale green. It has an index of refraction of about 

 1.62 and preliminary chemical tests indicate that it is near the chlorites in 

 composition. A further study of the mineral is being made. In the center 

 of the veinlets are irregular crystals of calcite and a little pyrite. 



A chemical analysis of the slate was made by Mr. George Steiger in the 

 laboratory of the United States Geological Survey and is given under No. i 

 of the following table. Analyses of several somewhat similar rocks and of a 

 sericite are also given. 



1234 s 



SiOs 54.49 5S-8o 60.28 57.96 55,00-67.00 



AI2O3 25.60 27.72 22.61 24.70 11.00-23.00 



Fe208 0.89 3.07 2.53 1.27 0.52- 7.00 



FeO 2.00 0.45 0.62 0.46- 9.00 



MgO 1. 18 0.53 1.3s 2.16 0.88-4.57 



CaO 1.90 0.14 0.13 2.30 0.33-5.20 



NasO 0.28 1.51 0.54 6.95 0.50- 3.97 



K2O 6.67 5-62 5.73 2.56 1.76- 5.27 



H2O — 0.33 0.60 0.04 



H2O -j- 3.91 4.03 3.62 1.06 2.82- 4.09 



TiOi 0.72 0.69 0.88 



Zr02 none 



CO2 I.S4 



C not det 0.97 



P2O5 0.08 0.03 



SOs none 



S 0.24 



MnO none .... tr. 



BaO none .... 0.04 



SrO none 



CuO tr. 



99.83 98.42 99.57 100.50 



Less O 09 



9974 



1. Middle Cambrian shale from British Columbia. 



2. Sericite. Durrberg. Quoted by Dana, System of Mineralogy, 6th 

 edition, p. 618, analyses 41. 



3. Mansfield slate (Lower Huronian). Crystal Falls District, Michigan. 

 U. S. Geological Survey Monograph 36, p. 59. 



