REPORT OF TEE CHIEF ASTRONOMER 



453 



SESSIONAL PAPER No. 25a 



The rock is a light bluish-gray, rather fine-grained syenite, breaking with 

 a sonorous ring. In the hand-specimen it shows a weak parallel structure, pro- 

 bably due to flow in the late magmatic period. A few small hornblendes and 

 many small feldspars twinned on the Carlsbad law, are arranged parallel to the 

 planes of the flow-structure. Minute biotites can also be detected macroscopi- 

 cally. 



Under the microscope the fairly abundant hornblende is seen to be a 

 strongly pleochroic, olive-green variety of great absorptive power. The biotite is 

 scarcely more than accessory. Nephelite, orthoclase, microperthite, microcline, 

 and probably soda-orthoclase [extinction of 8° on (010)] are the light coloured 

 essentials. The list of accessories includes melanite, apatite, and titanite. 

 Iron oxides are absent or are present in but the barest traces. 



The rock is very fresh, even the nephelite showing little alteration. In 

 this case the relations of the melanite point to its being a primary mineral. 

 The rock has been little, if at all, crushed since it crystallized. The garnet 

 is generally poikilitic, enclosing feldspar granules, and seems to have been the 

 last product of crystallization. A little anatase, probably derived from the 

 titanite, was observed. 



The chemical analysis of this specimen (No.1109) gave Professor Dittrieh 

 the following result: — 



Analysis of nephelite syenite, Kruger alkaline body. 



Si0 2 



Ti0 2 



A1,0, 



Fe 2 0, 



FeO 



MnO 



M R 



CaO 



Na,0 



K 2 



H,0 at 110°C. . 

 H,0 above 110°C. 



P 5 B 



CO, 



Mol. 



5511 



918 



•48 



006 



21-28 



209 



2-64 



016 



1-29 



018 



•08 



001 



•59 



015 



2-82 



050 



6-24 



101 



8-36 



089 



•14 





•58 





•27 



002 



•08 





Sp. gr. 



99-96 



2-666 



The calculated norm is: — 



Orthoclase. . 



Albite 



Anorthite.. . 

 Nephelite.. . 

 Diopside. . . . 

 Wollastonite. 

 Magnetite.. , 

 Ilmenite.. .. 

 Hematite. . . 

 Apatite. . . . 

 Water 



49-48 



13-62 



5-28 



21-30 



3-23 



1-04 



302 



•91 



•48 



•62 



•72 



99-70 



