Crystallization of Parisite. 



553 



Chemical composition. — The almost universal contamination 

 of the aegirite with other minerals made the ohtaining of suit- 

 able material for chemical analysis very difficult. By means of 

 magnetic and heavy solution separations combined with hand- 

 picking under the microscope, about three grams of material 

 were finally obtained which showed as impurities only a little 

 ilmenite and traces of octahedrite and quartz. 



The analysis made in duplicate averaged as follows : Aegir- 

 ite, Fallon Quarry, North Common Hill, Quincy, Mass., 

 U. S. A. (analyst, Warren). 



SiO 



Per cent. 

 51-73 

 •64 

 1-91 



31-86 



■87 



•60 



•87 



•14 

 11-43 



•40 



•20 

 none 



Molec. 

 •862 

 •008 

 •018 ) 

 •199 j 

 •012 ) 

 •008 | 

 •015 1 

 •003 .' 

 ■184 | 

 •004 J 



ratios. 

 0-862 



TiO a 



Al f O, 



Fe 



0-008 

 0-217 



2 3 



FeO 



MnO 



CaO 



MgO 



NaO 



0-226 



K 2 



H,0 



F 





Total 



Spec. grav. at 25° C. 



= 100-65 



= 3-499 



Although a portion of the Ti0 2 was probably present as 

 Ti0 2 (octahedrite), most of it is combined with RO as ilmenite, 

 and after deducting the Ti0 2 and the proportionate amount of 

 RO as ilmenite, the combined ratios are : Si0 2 = 0*838, R o 3 = 

 0-217, RO + R.,0 = 0-218 ; or very nearly Si0 2 : R 2 3 : RO + 

 R 2 0=4 : 1 : 1, leading to the formula (R" 2 R) Fe 2 Si 4 I2 . So 

 far as known to the writers, the ferrous iron is lower in this 

 aegirite than in any other hitherto analyzed, and the compo- 

 sition approaches very closely to the theoretical composition of 

 the compound, Na 2 Fe 2 Si 4 I2 , which is Si0 2 , 52 per cent; Fe 2 3 . 

 31-6 per cent; ]STa. 2 0, 13"4: per cent. 



Fig. 9. 









Fig. 



8. 







a 





e. 





rj 



r^JL_ 



a 



itv[ 







\r 



Figs. 8, 9. Ilmenite. 



Ilmenite. — Ilmenite occurs in moderate abundance in 

 both the Ballon and Fallon pegmatites. It appears to have 



