694 



SUBANTARCTIC ISLANDS OF NEW ZEALAND. 



[Geology. 



patches. It has the normal pleochroism for the mineral — (c) indigo blue, (6) dark 

 blue, (a) yellow. 



A third specimen has a banded structure. The dark bands proved to be a trans- 

 parent glass which includes minute idioniorphic crystals of olivine. The white 

 bands are composed of interlocking crystals of quartz with a little brown glass 

 between them. It appears as though the volcanic glass had been forced between 

 the quartz laminae of a schist. 



At Filhol Point, in Perseverance Harbour, near the observatory, a pale reddish- 

 grey rock crops out at the sea-level. There is a distinct shimmer on the fracture 

 of the rock, denoting the presence of numerous parallel feldspars. Sections show 

 an indefinite micro-spherulitic structure. The feldspar is all sanidine. Minute 

 aegerine granules occur, and there are irregular crystals of riebeckite. There is a 

 considerable number of minute yellow laths, seldom more than 0-2 mm. in length, 

 and extremely narrow. Refractive index high. Cleavage good. The ether axes 

 a and b lie in the lath-shaped sections, and the extinction is not quite straight (3) 

 in some sections. No pleochroism. These characters show that the mineral is 

 mosandrite, an identification that is supported by the fact that zirconium was found 

 by analysis. 



Analysis. 

 SiOa 



Al.Og 



¥e,0, 



FeO 



CaO 



MgO 



ZrO, 



TiOa 



Na02 



K2O 



H,0 



69 02 



1532 



4-29 



051 



032 



Oil 



0-16 



0-40 



547 



434 



1-86 



100-80 



This appears closely allied to pantellarite. 



Phonolite. 



A dark-grey rock, with a distinct shimmer on the fractured surface, owing to 

 the abundance of cleavage-surfaces of feldspar. 



Section : Though even-grained, the rock is not very fine -textured. Sanidine is 

 the dominant mineral. The crystals usually show Carlsbad twinning. Between 

 the feldspars a good deal of aegerine, with the usual pleochroism. With the aegerine 

 is some cossyrite and riebeckite, but the latter is much changed to a brownish-yellow 

 substance. A little magnetite occurs with the cossyrite. Though not seen in sec- 

 tion, a little nepheline is apparently present, for crystals of salt are obtained when 

 solution obtained by treatment of the rock powder with hydrochloric acid is evapo- 

 rated. 



