Turner — Rock-forming Biotites and Ampkiboles. 297 



purposes of comparison Ko. 2179, given in the table of 

 amphibole analyses, may be substituted, as this is from the 

 same area and represents the average rock. 



A comparison of the biotite analyses given in the table with 

 those of the rocks from which the micas were obtained, does 

 not suggest any very definite relations. These micas are all 

 quite similar in composition. It may be noted, however, that 

 the biotite richest in alumina and alkali is from the most acid 

 rock of the series, the biotite-granite (No. 2136). This rock 

 contains no amphibole. Biotites 1751 and 2652 are richer in 

 magnesia. Both of these are very similar in composition as 

 well as in color and pleochroism, and both of them are asso- 

 ciated with amphibole. 



Analyses of A 



mphibole 



and the containing rocks. 







1 



I ■ 



Quartz- 



Amphibole 







Amphibole Gabbro 



[Amphibole 



monzonite 



Donegal 



Donegal 





1970 1970. 



2652. 



2199. 



granite. 



granite. 



SiO-. 



46*08 47-27 



47-49 



1-21 



66-83 

 •54 



47-25 



58-04 



TiO, 



•77 



•92 





ZrO n -- 



10-56 



20-82 



none 

 707 



•04 



•04 

 15-24 



~5 : 65" 





AloO» - 



16-08 



Cro0 3 



faint trace* 



-02 





Vo0 3 -- 



_ 



FeoOs --- 



2-81 1-85 



4-88 



2-73 



19-11 



8-27 



FeO 



8-30 4-26 

 •15 trace 



10-69 

 •51 



1-66 

 •10 



•94 



1-70 



0-45 



MnO 



1-12 



NiO and CoO 



none 



- -02 











CaO 



12-64 1302 



11-92 



3-59 



11-76 



6-52 



SrO 



none trace 



none 



•03 







BaO..-. 



none none 



none 



•11 







MgO. ----- 



14-40 6-44 



13-06 



1-63 



11-26 



294 



KoO 



•34 -22 

 1-62 2 75 



•49 

 •75 



4-46 

 3 10 



1-04 



•98 



2-21 



Na.,0 



4-65 



Li.,0 



none none 

 •17 -08 



trace 

 t 



trace 

 none 







H 2 below 110° C.__ 





H 2 above 110° 0... 



1-97 1-27 



1-86 



•56 









P 2 5 



•18 -74 



none 



•18 







CO.. 



none 





trace 







FeSo 



-20 



I 









S0 3 







none 







CI 



trace 



i 



02 









F 



none 





•06 











Total 



99-99 



99-86 



! 100-05 



100-82 



99'69 



100-28 



Analyst 



Valentine 



Stokes 



Hillebrand 



Valentine 



Haughton 



Haughton. 



An examination of the powder of amphibole 1970 shows 

 that it contains a few grains of labradorite but otherwise appears 



* Cr 2 3 and V 2 3 determined by Dr. Hillebrand. 



f Dried at 105° C. before analyzing. No rare earths or zinc present. 



Am. Jour Sci.— Fourth Series, Vol. VII, No. 40.— April, 1899. 

 20 



