50 



Penfield and Stanley — 



to X as summarized on page 42. The relations, moreover, are 

 not materially altered if the titanium is regarded as Ti 2 3 , 

 when the excess of oxygen recorded in the analysis as Ti0 2 

 would be just about sufficient to convert the FeO and MnO 

 of the analysis to sesquioxides : according to the latter interpre- 

 tation the sesquioxide quotient becomes '128, and the ratio 

 of Si0 2 : RO = l : 1*21. With the high percentage of fluorine: 

 in the mineral it seems necessary to assume that some of it is 

 united with a bivalent element, magnesium for example, to 

 form a radical [MgF] ; and according to this assumption a 

 balance may be struck so as to leave a final residue in which 

 SiO„ : RO = l : 1. The interpretation is as follows : — 



Ratios 



"MgFl ' 

 _MgFJ 



' Resi- 

 due 



~Si,Ti]0 2 -778 

 = Al,Fej„6 3 -115 



—•038 



•740 

 •115 



= Fe,Mn,Mg]0 '540 

 OaO -227 



— •076 



•464 



•227 



[K,Na] 2 -058 

 H 2 -037 







•058 

 •037 



F. -072 



—•038 



•034 



"Al— F" 

 >0 



_ A1 — F . 



— •034 

 —•034 



•034 



Resi- 

 due 



<"<l* 



Na"] 



L 



A <o_i 



•706 

 •081 

 •464 



•22'7 ) 

 •058 \ 

 •037 



*0— NaJ 



—•081 



—•081. 



—•081 



—•081 



Resi- 

 due 



•625 



•383 

 •204 



•037" 



Total RO '624 



Proportion of radicals and remaining bases : — 



MgF']„0 

 Af a 0F" o "|"0 



Al„0 4 KNa,]"0 

 Fe;Mn,Mg]0 

 CaO 



HO 



Ratios 

 •038 

 •034 

 •081 

 •383 

 •204 

 •037 



•777 



Per cents 



4-9 



4-4 



10-4 



49-3 



26-2 



4-8 



100-0 



The final result here again shows 25 per cent (a little over) 

 of the hydrogen atoms replaced by calcium. 



In analysis I there was noted a slight excess of< fluorine over 

 that required by the alumina to form the radical [Al 2 OF 2 ]", 

 and it may be assumed that a very small amount of the radi- 

 cal [MgF] is present in that variety of tremolite. 



Summary and Conclusion. — The chemical composition of 

 am pinhole can be explained by assuming that it is based upon 

 a metasilicate molecule, which is, however, undoubtedly of a 

 multiple and complex nature. The uniformity in crystalliza- 

 tion of the different varieties in spite of the fact that they 

 show a wide range in their chemical composition, is a strong 



