GEOLOGY AND PETROGRAPHY OF THE PROSPECT INTRUSION. 477 



Minerals Present. 







Convctnd for decomposition. 



By weight as 



measured. 



Felspar 



44*8 



Felspar 



35-1 



Augite 



34*2 



Augite 



34*2 



Olivine 



8'2 



Serpentine 



12-4 



Biotite 



7*1 



Biotite 



7*4 



Iron Ores 



5*6 



Iron Ores 



5*8 



Apatite 



0*1 



Analcite 



4*9 



• 





Chlorite 

 Apatite 



O'l 

 0*1 





lOO'O 



Specimen C. 100*0 



As the composition of this rock appeared very constant 

 throughout, only a small number of crystal measurements 

 (about 150) were made. Careful microscopic examination 

 shows that a little chlorite and chloritoid are mixed with 

 the serpentine, hence in correcting for decomposition the 

 chlorite has been taken as 0*8 and the serpentine as 11*7. 



The augite is pinkish-brown in colour, hence titaniferous, 

 and sections vary in outline from idiomorphic to hypidio- 

 morphic. Both augite and felspar contain inclusions of 

 apatite and biotite, and sometimes of ilmenite. 



The plagioclase varies from oligoclase to basic labradorite. 

 Many of the larger crystals show zoning, the extinction 

 angle varying from the outside inwards. The felspar is a 

 good deal decomposed, being penetrated by strands of 

 chlorite, and in the more acid parts by broader veins of 

 analcite. 



The analcite contains inclusions of apatite (see Plate 

 XXXIX, fig. 3), and occurs both where decomposition has 

 been great and where it has been slight. In some cases it 

 is undoubtedly secondary after felspar, in other cases there 

 is no evidence to prove its secondary origin. In the latter 

 cases augite, serpentine pseudomorphs and felspar present 

 idiomorphic outlines towards patches of analcite which are 

 fairly regular in shape. Even in these cases we find 

 numerous needles of apatite included in the analcite proving 



E 1— Dec. 6, 1911. 



