FROM THE (ACHE. DEPOT ISLAND, ANTARCTICA 237 



Basic Enclosure in Granite of Depot Island 



Crystallinity : holocrystalline. 



Grain size : relative — fine to medium : absolute — -5 to 1-5 mm. 

 Fabric : granitoid. 



Minerals present in decreasing order of abundance ; labradorite, biotite, apatite, 

 sphene. 



The labradorite is rather basic, having an extinction angle of 25° on the symmetrical 

 albite twins. This corresponds to a composition Ab 7 An 13 . 



The biotite is a deep brown variety, intensely pleochroic. There is a suggestion of 

 parallelism in the arrangement of the prismatic flakes. 



A few small crystals of apatite are present. 



No sphene was observed in either of the two slides examined, but some large por- 

 phyritic crystals, 6 mm. x 4 mm. were observed in the hand-specimen. 



The rock is an uncommon type, being a pure mica diorite with sphene. 



