THE METAMORPHIC ROCKS OF ADEL1E LAND. 8TILLWELL. 123 



No. 981. This is the specimen of the dark amphibolite, showing massive texture 

 with fine even-sized grains of hornblende and felspar. In section it shows affinities 

 to the Cape Denison amphibolites, and its percentage mineral composition is 



Hornblende 34-5 



Felspar 50-3 



Epidote 6-5 



Biotite 5-1 



Sphene 2-4 



Apatite 0-8 



Iron ore 0-4 



Calcite present 



This composition possesses marked differences from the Cape Denison amphibolites. 

 The proportions of hornblende and felspar are approximately reversed. The composition 

 is most like that of the epidote biotite schist (No. 153), except that the biotite is replaced 

 in this rock by hornblende. The high percentage of felspar is reflected in the colour 

 of the hand specimen, which is not the dense black of the Cape Denison rocks. A 

 portion of the felspar is saussuritised, and an extinction angle in partly saussuritised 

 crystals of 40 has been measured from the lamellae, and hence it may be called 

 labradorite. There is a considerable amount of clear felspar which may bear a trace 

 of lamellar twinning and which has a refractive index often inseparable from the Canada 

 balsam. This clear felspar is looked upon as albite. No quartz has been detected 

 among the clear felspar. 



The hornblende is a little paler in colour than in the Cape Denison rocks, but the 

 bluish tinge is prominent. The edges of the crystals are more ragged and indefinite. 

 Epidote is found in pleochroic crystals of the same size as the hornblende. It may be 

 associated with the hornblende in a manner which suggests its derivation from the 

 hornblende, and it may fringe the biotite crystals. Crystals with definite crystal 

 boundaries may be set in the biotite plates, and they may contain a brownish nucleus 

 of allanite. 



The biotite appears in relatively large and broken plates, and has a greenish-brown 

 colour in its darkest position. It contains pleochroic haloes. Sometimes it is fringed 

 with a rim of opaque iron ore, which is in turn surrounded with epidote. This suggests 

 that free iron oxide is set free in a reaction between felspar and biotite. Sphene and 

 apatite are abundant accessories, and occasional plates of calcite are present and are 

 included in the felspar percentage. 



The rock may be called an albite amphibolite, and is placed in the family of albite 

 amphibolites in the epi division of the Group of the Eclogites and Amphibolites. 



