352 



THE PENOKEE IRON BEARING SERIES. 



Analyses of feldspars. 



HjOat 105° 



HiO at red heat. 



SiOj '... 



Alj03 



Fe,Oj 



FeO 



MnO.. 



CaO 



MgO 



KjO 



NajO 



119 

 5118 

 27-00 



3-lB 

 (*) 



■17 

 11-70 



1-92 

 -41 



3-48 



100-24 



-03 



-54 



51-99 



29-32 



1-23 



(*) 



trac«. 



12-60 



-63 



■28 



2-91 



99.53 



-13 



-64 



56-15 



■20-05 



1 98 



(*) 



-13 



8-70 



-54 



1-56 



4-79 



100-67 



-95 



01-65 



19-91 



2-28 



(*) 



trace. 



4-12 



-61 



5-72 



4-74 



99-98 



* Undetermined. 



According- to Zirkel's Jlineralogie, p. 682, AljAiio has the following 

 composition: 8iO,, 51-34; AlA, 31-20; CaO, 13-67; Na^O, 3-79. In No. 

 1, it will be seen that, if the alumina and ferric oxide are put tog-ether, 

 the calcium and magnesium counted as tlie protoxide base equivalent to 

 calcium, and tlie sodium and potassium l)e put together, this analysis 

 corresponds almost exactly to the above theoretical calculation. Therefore 

 it may be considered as very close to AljAu.,, which, under the present 

 accepted nomenclature, makes the feldspar labradorite. 



According- ti» the same authority ALAuj has the following composi- 

 tion: SiOo, 53-01; Al.,();„ 30-06; CaO, 12-36; Na.,0, 4-57. The composition 

 of AliAn, has just been given. Combining percentages in the same way 

 as before, it will be seen that No. 2 is intermediate in composition between 

 AlaAuj and AljAua, which again makes the feldspar labradorite. 



From the same authority AI4 An 3 has SiO,, 57-37; AlA, 27-12; CaO, 

 8-92; NagO, 6-5!). Making allowance for the water contained in 3A, and 

 combining as in the previous case, it is seen that this analysis corresponds 

 very closely to this theoretical composition, which would place this feldspar 

 at the acid end of the andesine series. The analysis of 3B, and particu- 

 larly the large amoiuit of ^^otassium which it contains, would seem to 

 indicate that we have here probably one of the anorthoclase series, and it 

 is possible that the percentage of 1-56 per cent of potassium in 3 A is 

 accounted for hy a mingling of anorthoclase and andesine. It is to lie 

 noticed that it is in the olivine diabase — that is, the rock which has an 



