Metamorphic and Plutonic Rocks at Omeo. 105 



most obligingly made the subjoined quantitative analysis of 

 this felspar in the laboratory of the Technological Museum: — 



Analysis 



No. 



1 . — MiCROPERTHITE.* 



SIO, 







021 3 



ALA •.. 







24-35 



Fe.A ... 







tr. 



Na.,0 







(jG6 



K.O 







8-31 



H^O 







•50 





10195 



The mica is the usual silvery coloured muscovite found in 

 these rocks, in plates, and in irregularly shaped crystals, 

 having an hexagonal, that is to sa}^, a modified rhombic 

 outline. When least altered, the cleavage plates have a 

 slightly smoky tint by transmitted light. The optical 

 characters of this mica are as usual, and it is according to 

 Reusch's test, a mica of the second order. 



I subjoin a quantitative analysis of this mica: — 

 Analysis No. 2. — Muscovite. 



Fl 



•15 



Si.O, 



44-67 



Al.,,0 



37-44 



Fe.A ... 



•48 



Fe.O 



•91 



Ca.O 



-26 



Mg.O 



•42 



K.O 



10-90 



Na.gO 



.. ^ ... 1-24 



H,0 



3-76 





100-23 



Hygroscopic Moisture ... 2*18 



Sp.gr. ... ... 2-758 



The quartz of this granite is somewhat glassy in appearance, 

 and contains numerous fluid cavities without bubbles. It 

 shows cloudy obscuration when examined by polarised light, 

 indicative of strain. 



* The grains of free quartz were picked out from the sample before analysis. 



