1921. No. 8. o\ the; eclogites of xorway. 



1 1 



There is, however, still another condition favouring the formation of 

 garnet. This mineral, as a constituent of the coronas, belongs to the stage 

 of hornblende-gabbro facies. Now, many of the norite and gabbro masses 

 in Southern Norway pass, towards their borders, gradually over into 

 hornblende-gabbro or amphibolite. To put it in the terms of the iacies- 

 principle, the boundary zones of these masses have crystallized under 

 conditions not far from those of the hornblende-gabbro facies. These 

 boundary zones often contain almandite, a mineral not appearing in the 

 typical gabbro facies, although its field of stability exceeds the upper 

 temperature limit of the pure hornblende-gabbro facies. Therefore we may 

 speak about an intermediate facies, at a certain very limited range of 

 variation in the composition characterized by the occurrence of almandite. 



This example, just as the other examples of garnet-bearing gabbros 

 and amphibolites of whose garnets anah'ses are available (cf. Mineral Facies, 

 p. 171), show invariably garnets with prevalent almandite. In this respect 

 they differ from the eclogites, and other rocks genetically connected with 

 eclogites (cf. p. loi), whose garnets var}- within a wide range between those 

 extremely high in almandite to those containing as much as 75 per cent 

 pyrope. 



