grains of picotite and also a little calcite are present, 

 analysis of this rock was made and given below (A). \ 

 it is the analysis (B) by Mr. J. C. H. Mingaye, of 

 diallage rock in the volcanic pipe at Norton's Basin on 

 Nepean 1 :— 





A. 



B. 2 



Norms. 



Si0 3 



5009 



50-36 



Orthoclase 



Al.O, 



11-31 



246 



Albite 



Fe 2 3 



191 





Anorthite 



FeO 



3 09 



4-41 



Diopside 



MgO 



13-83 



20 76 



Hypersthene 



CaO 



15-63 



6-25 



Olivine 



Na 2 



1-92 



•51 



Magnetite 



K 









H 2 0- 



•61 



2-21 



Chroraite 



H 2 + 



1-06 



407 



Carbonates 



co„ 



16 



4-41 



Quartz 



Ti0 3 



•95 





Water 



Cr 2 3 





04 





NiCoO 





•31 



1( 



MnO 



•06 



•29 





100-83 100-38 



The most unexpected feature in the Dundas diallage rock 

 is the high percentage of alumina. A previous partial 

 analysis of this specimen had been rejected as incorrect, 

 chiefly because of this feature, but a re-analysis confirmed 

 it, giving the figures shown. It is, however, not the highest 

 recorded for diallage, though those with higher alumina 

 have often much higher iron content and are poorer in 

 silica. Some chrome diopsides have somewhat similar 

 composition.' 



But as the specimen on its boundary was intersected by 

 basalt veins proceeding from the basalt in which it was 



and F a 



1 Dana, System of Miners 

 Handbuch der Mineralogie, 



