I92I. Xo. 8. ON THE ECLOGITES OF NORWAY. 8s 



Ca.\l,Si.>0, - Mg.SiO, = MgXaALSi^O,,. 

 Anorthite 4- olivine -- garnet. 



Though it is quite possible that garnets having strictly the composition 

 postulated by this equation may exist in some eclogites, this is, however, 

 not the case here, as our garnet contains much less lime. The reaction 

 actually was more complicated. 



The inclusions of olivine-rock must be regarded as primary earlv segrega- 

 tions from the magma, and the boandar}- zones were formed probabh' before 

 the labradorite-rock was solidified. This presumption is closest at hand, 

 and nothing points to the contrary. The occurrence of the same kind of 

 garnet as primary crystals in the unaltered labradorite-rock proves that the 

 conditions of existence of garnet were already present at the magmatic stage. 



The hornblende, on the other hand, is clearh- posterior to the garnet, 

 though it may possibly have crystallized earlier than the labradorite. It is 

 much of the same nature as the kelyphite zones in many eclogites, and the 

 occurrence of spinel also conforms to this view. 



Garnet in Labradorite-rock in Indre Sogn. 



As already pointed out, the Sogn labradorite-rocks often contain garnet. 

 There are t\vo modes of occurrence of this mineral: either in dark segrega- 

 tions together with other mafic minerals, and as single idiomorphic crystals. 

 Both these kinds are represented in the upper part of Krokedalen, where, 

 according to J. Rekstad^ "the rock consists of reddish violet labradorite 

 with frequent lenses and layer-shaped masses of green colour. The rock 

 contains, in the light feldspar portions as well as in the dark hornblende 

 portions, considerable amounts of garnet". 



I have had thin sections made of several specimens of both kinds 

 kept in the Museum in Christiania and will briefly describe a few 

 examples. 



A specimen of "eclogite" from Fodnes, Laerdalsfjord, collected 

 by Th. Kjerulf, represents the dark inclusions I fig. 13). It is a medium- 

 grained and foliated rock in which quite small lenticular veinlets of feldspar 

 are visible to the naked eye. It is composed of hypersthene, garnet and 

 plagioclase besides much iron ore and a little brown hornblende. 



The crvstals of hvpersthene are surrounded by granulated zones ot 

 the same mineral, and where several crystals have been aggregated together, 

 there the structure is mortar-like. The crystals of garnet, on the other 

 hand, are rounded as though corroded and always surrounded by zones 

 of granular feldspar with iron ore. This feldspar is pure plagioclase, while 

 the feldspar in the small veinlets is antiperthite. 



' Op. cit. "X. G. U. Aarbog 1907, Vllt p. af 



