GEOLOGY AND PETROGRAPHY OF THE PROSPECT INTRUSION. 545 



Mineral. 



Mols. x Molec. 



weight. 





Weight. 



Percentage wt 



Orthoclase 



•004 x 



556 





2-22 



2*3 



Albite 



•037 x 



524 





19-39 



20*0 



Anorthite 



•055 x 



278 





15*29 



15*7 



Si0 9 



•010 x 



60: 



= •600 











A1 2 3 



•003 x 



102 : 



= '306 











Fe<>0 3 



•001 x 



160 : 



= •160 









Biotite i 



FeO 



•003 x 



72: 



= '216 



• 



1*70 



1*7 





MgO 



•005 x 



40: 



= •200 











K 2 



•002 x 



94: 



= •188 









m~ 2 o 



•002 x 



18: 



= •036 J 











1*702 





/Si0 2 



•307 x 



60 



18*420] 









A1 2 3 



•021 x 



102 



2*142 









Fe 2 O s 



•007 x 



160 



1*120 







Augite i 



FeO 

 MgO 



•037 x 

 •121 x 



72 

 40 



2*664 

 4-840 



> 37-18 



38*2 





OaO 



•138 x 



56 



7*730 









Na 2 



•003 x 



62 



0*186 







lTi0 2 



•001 x 



80 



0'080j 

 37*182 









Si0 2 1-032 x 



60 



1*920) 







Olivine 



FeO 



•031 x 



72 



2*232 



5*47 



5-7 





MgO 



•033 x 



40 



1-320, 









5*472 





Ilmenite 



•054 x 



152 





8*31 



8*4 



Magnetite 



•032 x 



232 





7*42 



7-6 



Apatite 





•001 x 



336 







•34 



•4 



97*22 100-0 



Sum of principal components in analysis : 95*85 + 0*36 

 H 2 + 1*26 deficient Si0 2 . 97'47 deficit 0*25. Compo- 

 sition of plagioclase: Ab 74 An 5 5 = Ab 4 An 3 . 



Mode of Specimen B. 

 In this specimen the quantity of biotite was determined 

 by the Rosiwal method, which gave 12*0 per cent. It is 

 found generally that the proportion of coloured constituents 

 is liable to slight exaggeration by that method, owing to 

 portions of the coloured mineral which overlap a colourless 



