15 



A specimen of the granite from Granite Island was 

 analysed, and the analysis is given below, along with that of 

 another South Australian microcline granite, for com- 

 parison: — 



I. II. 



SiO. ... 



68-20 



68-31 



AL03 



15-99 



15-21 



Fe..03 



0-89 



0-53 



Feb ... 



2-58 



3-73 



MgO ... 



0-80 



0-65 



CaO ... 



2-61 



1-99 



Na.,0 ... 



2-85 



3-14 



K.O ... 



4-60 



4-68 



h;o+ 



0-64 



0-44 



h:o- 



0-21 



0-08 



c6., .. 



abs. 



abs. 



Tid., ... 



0-58 



0-53 



P.O". ... 



0-14 



0-29 



MnO .. 



0-04 



0-04 



BaO .. 



0-04 



abs. 



ZrO. .. 



p.n.d. 



— 



FeS; ... 



0-11 



0-09 



CI " ... 



— 



0-10 



Total 



... 100-28 



99-81 



(10) Sp.gr 



. atl9°C 2-673 





IT. 



Porphyritic granite from Granite Island. 

 W. R. Browne. 



Granite, Hundred of Moody, Co. Jervois, 

 Pen. Anal. W. S. Chapman. dD 



Anal. 



Eyre 



An approximate mode calculated from the analysis gave 

 the following weight-percentage composition 



Quartz 



Microcline 



Plagioclase 



Biotite 



Ilmenite 



Apatite 



Other minerals 



(Ab,,) 



28-9 



23-3 



29-8 



16-3 



1-2 



-3 



-2 



Certain assumptions had to be made in arriving at this 

 result. All the MgO and FeO were allotted to biotite, and 



no) The standard of comparison is water at 4°C. 

 (U) Geol. Surv. of S. Austr., Bull. No. 3. Geology of the 

 Co. of Jervois, by R. L. Jack, B.E., F.G.S., p. 14. 



