380 



BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



Analysis and ratios of chlorite from near Challis 

 (E. V. Shannon, analyst) 



Silica (Si0 2 ) 



Alumina ( AI2O3) - - - 



Ferric iron (Fc20s) 



Ferrous iron (FeO) 



Manganous oxide (MnO) _ 



Lime (CaO) 



Magnesia (MgO) 



Water (H 2 0) above 110° C 

 Water (H2O) below 110° C 



Total 



Per cent 



30.76 

 12.12 



9.12 

 22.76 



1.24 



Trace. 



12.36 



9.76 



1.80 



Ratios. 



0. 510 0. 170X3 

 119\ 



.057/ 



.317 



.018 



, 176X1 



1.00X3 

 1.03X1 



.160X4 .94X4 



.307) 



; ^}. 160X4 



.94X4 



99.92 



This analysis yields the formula 4(Fe,Mg)0.(Al,Fe) 2 O s .3Si0 2 . 



ALO, = 1:2. This can not 



4H 2 0. 



With FeO : Mg = 1 : 1 and Fe 2 3 



be definitely assigned to any member of the chlorite group, but is 

 most closely related to diabantite and delessite, chlorites occurring 

 characteristically as amygdule fillings in basic igneous rocks. The 

 high content of ferric iron may in part be secondary and due to oxi- 

 dation of a part of the iron originally present as ferrous oxide. 



Heated in the forceps before the blowpipe this chlorite exfoliates 

 somewhat, becomes magnetic, and finally fuses with some difficulty 

 to a black magnetic slag. In the closed tube it yields abundant 

 water having an acid reaction, indicating a small fluorine content. 

 It is quickly and completely soluble in hot 1: 1 hydrochloric acid. 



In the same specimens there occurs a second chlorite which never 

 completely fills the cavities but merely forms a thin lining 0.5 mm. 

 or less in thickness in cavities containing fillings of mordenite and 

 serves as a coloring matter in the surrounding andesite. It is impos- 

 sible to obtain enough of this material in pure form for analysis. It 

 is deep blue-green in the specimen and under the microscope is seen 

 to consist of finely felted shreds and scales of a deep blue-green color 

 which, in the aggregate, do not show any noticeable pleochroism. 

 The indices of refraction are a =1.606, 7 = 1-608, birefringence 

 7- a = 0.002. This chlorite differs from the preceding both in color 

 and birefringence. 



LEMHI COUNTY 



Green micaceous rosettes associated with apatite in porous schist 

 in the cobalt ores of the Togo property, in the Blackbird district, 

 consist of a chlorite which is biaxial and positive with 2V nearly 0°. 

 The acute bisectrix is normal to the basal plates and the refractive 

 index, is is about 1.620. The mineral is pleochroic with X and Y 

 blue-green and Z greenish brown. This chlorite is not appreciably 

 decomposed by boiling with 1 : 1 hydrochloric acid. 



The specimens consisting largely of chloritoid from the Nickel 

 Plate property, in the Blackbird district, which have been described 

 above under chloritoid, contain a considerable amount of a green 



