1915- ^O- 4- REPORT OX ROCK-SPECIMEXS. I9 



The plagioclase shows zonal structure with increase of An from the 

 border to the central nucleus. According to the extinction angles «' measured 

 in sections _ the axis a the percentage of anorthite is calculated to: 

 .•Vn;j3 — An-,; . The central nucleus is labradoriU and the margin andesine. 

 In the sahl-band a plagioclase of the same composition is the only felspar. 



Biotite shows strong absorption: ß and y dark brown, « light straw- 

 yellow. Included in biotite are shown p\Tite. magnetite, zircon and apatite. 



The quartz is cracked and shows undulatorv' extinction. The central 

 part of the quartz-grains is filled with inclusions as is usual in pegmatite- 

 quartz : the borders of the grains on the other hand are iree from 

 inclusions. 



Apatite occurs sparingly. A few coarser grains are seen in the middle 

 part of the pegmatite; in the sahl-band the contents of apatite are more 

 prominent. Zircon, pyrite and magnetite are present in small amounts. 



The specimens show onl\- the pegmatite bordering on the amphibolite 

 as described below. Along the border a band of black biotite is shown 

 about I cm. thick (Fig. 6). The contents of the black biotite is also prominent 

 in the neighbouring part of the amphibolite along the junction. 



In my opinion the most reasonable explanation of the segregation of 

 biotite along the border of the pegmatite and in the neighbouring part of 

 the amphibolite is, that it is caused by pneimaatoh'tic effect of the intruding 

 granite magma on the basic rock. My experience from studies of the 

 granite-pegmatites (felspar-quarries! in Southern Norway* reinforces the 

 above explanation. The great dikes of granite-pegmatite often penetrate 

 basic rocks, such as araphibolites and gabbros. Along the borders of the 

 pegmatite the basic rock is recrystallised into micaceous rocks of rather 

 coarse grain. Fragments of amphibolites of different size included in the 

 pegmatite are shown all through recrjstallised to scal\' masses of biotite. 

 The chief agency- is certainly the magmatic aqueous solutions. 



The above mentioned "Augenstructure" characteristic of the micaceous 

 sahl-band is shown under the microscope to be due to the arrangement 

 of the biotite-scales along the borders of the coigns of the plagioclases. 

 I Fig. 8.) 



One specimen of the micaceous sahl-band shows segregation of magnetite, 

 occurring in rather coarse-grained aggregates sometimes with small nuclei of 

 p\Tite, and including idiomorphic grains of zircon and apatite, scales of 

 biotite and muscovite, as well as some few grains of felspar and quartz. 

 The plagioclase is oligoclase. AbvAn^. Orthoclase partly altered into m\Tme- 

 kite and muscovite is rare. The zircons included in biotite are surrounded 

 by fine pleochroic halos. (Fig. 9.1 



