90 



PROF J. H. L. VOGT ON XABEADORITE-NOEITE [May 1909, 



Taking into consideration the fact that the porphyritic plagioclase 

 amounting to 23 per cent, consists of 61 anorthite, 33 albite, 

 6 orthoclase, and that the plagioclase amounting to 62 (or 61-88) 

 per cent, in the 77 per cent, of ground-mass consists of 52 anorthite, 

 42 albite, 6 orthoclase, the components of the whole rock are 

 thus : — 



- n .,- , , - i f38"81 percent. CaAl.oSi"08 



70-b5per cent, plagioclase I - 



(An,Ab,Or) 



I 424 



i.\a.o.ioj3W8 

 KAlSi 3 8 







7'0 per cent, titano- 



/ 6-3 

 I 0-9 



Fe 3 4 







magnetite 



FeTiO.3 









( 6-0 



Mg 2 Si 2 6 x 

 Fe 2 Si 2 6 









i 2-0 , 







10 per cent, hypersthem 



i 1-3 , 



Ca~FeSi 2 O fi 



60 per 



cent, Mg 2 Si 2 6 





| 0-46 , 



FeAl 2 Si0 6 



60 



CaMgSi 2 





i, 0-23 , 



FeFe o Si0 6 



._33 



_ 30 



CaFeSi 2 O e 





( 6-0 



Oa'MgSi 2 6 



Fe 2 Si 2 6 





| 2-0 



CaFeSioOe 



1-1 



FeAl 2 Si0 6 



10 jDer cent, diallage .. 



i ro , 



1 0-6 



{ 0-38 , 



Fe 2 Si 2 6 

 FeAl 2 Si0 6 



FeFe 2 SiO G J 



06 



FeFe 2 SiO G 



23 per cent, biotite 



f several c 

 l small 



Dmponents in 









quantity. 







l 0'09 per cent, apatite. 



On the Order of Crystallization. 



It is evident that the labradorite-phenocrysts were separated out 

 before the interstitial minerals. Farther, it may be presumed that 

 the crystallization of the very large phenocrysts began at a some- 

 what earlier stage than the smaller phenocrysts occurring between 

 the large ones. 



The crystallization of the labradorite began at certain points 

 (' centres of crystallization ') lying from 8 to 18 centimetres apart. 

 And, when this crystallization had gone on for some time, a crystal- 

 lization of plagioclase began round new centres. The inclusions in 

 the phenocrysts are dealt with below. 



When the separation of the phenocrysts had come to an end, the 

 ground-mass began to solidify, this taking place at first with 

 a contemporaneous crystallization of magnetite and labradorite. 

 That the magnetite crystallized before the mica and the pyroxene- 

 minerals is seen from the fact that the latter are frequently 

 deposited round the magnetite-individuals. It is further very 

 frequently observed that a particularly large quantity of magnetite 

 occurs immediately round the margins of the labradorite-pheno- 

 crysts, this being the case with the small as well as with the large 

 ones. In a zone about 5 millimetres broad round the labradorite- 



