92 PE0E. J. H. L. VOGT ON EABEADOEITE-NOEITE [May 1909, 



only about 0-01 per cent., occurs as inclusions in the magnetite. 

 The crystallization of the spinel probably took place after the 

 separation of the labradorite-phenocrysts had been completed. 



Quite small quantities of apatite are sometimes observed in 

 microscopic sections of the ground-mass, but never in the numerous 

 slides prepared from the labradorite-phenocrysts ; this is an in- 

 dication that the crystallization of the apatite began relatively late. 

 A definite conclusion on this question is, however, not possible in 

 the present case. 



The labradorite-phenocrysts contain, besides the ordinary micro- 

 lithic interpositions, some inclusions of magnetite, biotite, hyper - 

 sthene, and diallage, these inclusions being estimated at about 

 one-half per cent, of the phenocrysts, in some sections rather more, 

 in others less or nothing at all. 



The minerals in these inclusions occur, according to estimation, 

 in the same proportions as in the ground-mass, but in much smaller 

 individuals, of only about one-fifth of the size of those in the 

 ground-mass. The enclosed minerals do not show idiomorphic 

 outlines against their ' host,' the plagioclase. The inclusions as a 

 rule lie with their longitudinal dimension approximately parallel 

 to the cleavage-planes — that is, the most important planes of 

 growth — of the plagioclase. Frequently the enclosed minerals are 

 accompanied by plagioclose in quite small individuals and having a 

 different orientation from that of the ' host.' In other cases, one 

 finds in the immediate neighbourhood of the inclusions plagioclase 

 having the same orientation as that of the 'host,' but a somewhat 

 different extinction-angle, thus showing some difference in chemical 

 composition. 



These inclusions are, according to the foregoing observations, 

 small portions of the mother-liquor, enveloped by the growth of the 

 plagioclase, and crystallized during the later cooling. We may 

 recall the well-known inclusions of glass, that is, of mother-liquor, in 

 crystals of leucite, etc. In these last cases the inclusions solidified 

 in an amorphous condition, but in the case of the labradorite-norite 

 the inclusions necessarily solidified in crystalline form just as in the 

 ground-mass, on account of the slowness of the rate of cooling. 

 The felspathic components present in the liquid inclusions, wAn, 

 •mAb, oOr, crystallized sometimes in small independent individuals 

 and sometimes in the same crystallographic orientation as the 

 ' host.' 



Physico-chemical Explanation of the Order 

 of Crystallization. 



To illustrate the order of crystallization in a ternary system 

 consisting of mutually independent components, I use a graphic 

 representation 1 (fig. 2 a), with a horizontal projection (fig. 2b). 



1 See, for instance, my paper on ' Pkysikalisch-chemische Gesetze der Krys- 

 tallisationsfolge in Eruptivgesteinen ' Tscberm. Min. Petrogr. Mitth. vol. xxir 

 (1905) figs. 3a & 3b, on p. 442. 



