72 



I'KN'ni KSKOI.A. M.-N. Kl. 



In all the s|>((iiii(Ms so far dcsciihcd aiii|)liil)r)les occur only as kelyphitic 

 shells (green lioniMcnde) arrxiiul the i^aiiK I and occasional large grains 

 (colourless actinolilc); they show no connection whatever with the myrmekite- 

 like intergrowth. 



When all the pyroxene has been changed into the intergrowth, this 

 may continue to grow coarse, and the difference between the front and the 

 basis tends to disappear. A specimen from Hegersk j a eret, Hustad- 

 \ikcn, i-epresents this final stage of develoj)nicnt (fig. i o, pi. 111. '1 he 

 pyro.xene shows 2 V y 60 . In this case the plagioclase .sometimes show's 

 twinning lamellae and, in sections J_ M, a maximum extinction angle of 10 '. 

 It is an oligoclase-andesine. 



This is the most peculiar kind of alteration in the x\orwegian eclogites 

 enclosed in gneiss. I will call the myrmekite-like intergrowth a symplectite, 

 according to the proposition of J. J. Sederholm'. 



Structuralh' this intergrowth shows the most i-emarkable resemblance 

 of the common (|uartz-plagioclase-mvrmekite. Many other kinds ot such 

 symplectites have been observed (summarized by Sederholm, op. cit.). 



The present case deser\es a special interest because the origin of this 

 diopside-plagioclase-symplectite is perfectly clear from the point of view ot 

 the facies-theory : The jadeite-bearing pyroxene became unstable, when the 

 pressure was reduced, and was replaced by the alkali-free diopside and the 

 soda-lime feldspar. It is true that the diminution of the percentage of soda 

 in the newly crystallized pyroxene has been not proven by any positive de- 

 termination; its axial angle in the chloromelanite-eclogite seemed to be 

 smaller than that of the chloromelanite, but I was unable to measure it 

 exactly. But considering the constant occurrence of this phenomenon in 

 the jadeite-bearing pyroxenes and its absence in the jadeite-free pyroxenes 

 from the eclogites in the dunite, and further the fact that the feldspar 

 makes up a smaller part of the intergrowth, just as jadeite in the unaltered 

 pyroxene, the above interpretation cannot be denied. 



It is not clear, why the alteration has chosen such a curious way ot 

 replacement and not a simple breaking up and separation of plagioclase, 

 as is the case in the solid solutions of feldspar: the perthite. This kind 

 of alteration, however, was also observed, being represented in specimens 

 from Gimnaes and from Trek rem near Ting\old, both localities in 

 Nordmore. In these the plagioclase has been separated out at the same 

 time in the whole of the pyroxene ma.ss, in the former in long and almost 

 linear rods parallel to axis c. 



This specimen from Gimnaes also shows incipient uralitization, green 

 hornblende forming zones around the pyroxene in homoaxial arrangement. 



j. J. Sederholm, On Synantctic Minerals and related Phenomena. Bull. Comm. g:eol. Fini. 

 N:o 48, 1916, p. 46. 



