Constitution of the Natural Silicates. 411 





Burgess. 



Edwards. 



Port Henry. 



SiO„ 



39-66 



45-05 



34-52 



Ti0 2 



•56 







2-70 



A1,0, 



17-00 



11-25 



13-22 



Fe 2 3 



•27 







7-80 



FeO 



•20 



•14 



22-27 



MnO 











•41 



(Co,Ni)0 











•30 



CaO 



none 











BaO 



•62 







. . 



M<?0 



26-49 



29-38 



5-82 



li;o 







•07 



•04 



Na 2 



•60 



•45 



•16 



K 2 



9-97 



8-52 



8*59 



H 2 



2-99 



5-37 



4-39 



F 



2-24 



• 



•34 



PA 



trace 







trace 





100-60 



100-23 



100-54 



Less 



•94 





•14 



99-66 100-40 



The fractional water determinations gave — 





Burgess. 



Edwards. 



Port Henry. 



[„0 at 105° 



•66 



' 



•57 



" 250°-300° 



•35 



•73 



•45 



" red-heat 

 " white-heat 



i 1*98 



•73 

 3-91 



I 3-37 



In all the analyses of this investigation, when much iron was 

 found, the total water was determined directly ; so that the 

 figures for the higher temperatures do not represent mere loss 

 on ignition. In these micas the percentages of constitutional 

 water, to be used in the discussion of formulae, are 1*98, 4*64, 

 and 3'37 respectively. 



In the Burgess phlogopite numerous inclusions were ob- 

 served, consisting of slender prisms, and at our request these 

 were examined microscopically by Mr. Waldemar Lindgren. 

 The mica, according to his examination, is made up of " thin 

 foliEe, under the microscope colorless, dark between crossed 

 nicols ; interference figure apparently a cross, not separating 

 into hyperbolas ; seemingly uniaxial, but with better instru- 

 ments it would probably be found to be biaxial with a very 

 small axial angle. Shows excellent asterism, caused by inter- 

 positions arranged in three directions cutting each other at an 

 angle of 60°. The inclusions are prisms of a strongly refract- 

 ing and bi-refracting mineral, so thin as to show brilliant 

 Newton's colors. In spite of the very small thickness, the 



