I9I5- N'o. 4- 



REPORT ON ROCK-SPECIMENS. 



From the figures I have calculated the following approximate mineral 

 composition : 



By this calculation are left small remainders of TiO^, Al^Oij and FeO. The 



major portion of K^O is used for calculation of the micas; the remaining 



0-39 ° of KqO, is calculated as orthoclase. Probably the plagioclase 



contains the small percentage of orthoclase, as potash-felspar is not shown 



in the rock. Calculated in this manner the mineral composition of the 



rock is : 



Quartz 39.31 " 



Oligoclase (Ab, C)r)3Ai . 51.96 ^ 



Mica 7.47 > 



Other constituents . . . 0.71 > 



Unfortunately the rest of the analysed rock-sample and also the 

 section were lost by an accident. Through the kindness of Dr. N. Sahl- 

 bom I obtained the rest of the rock-powder not used for the analysis, 

 and at my request Miss Mimi Johnson kindly undertook the separation of 

 this powder with heavy liquids. The result was as follows: 



3.96 gr. of the rock-powder was treated with Thoulet's liquid. It 

 was found : 



0.24 gr. 1= 6 "^ 0) mica and accessories with Sp.gr. >2.70 



the rest 3.72 gr. 1= 94 ° 0) felspar and quartz with Sp. gr. | ^ ^'i^ 



Miss Johnson! also determined the mean réfringence of the felspar 

 by the method of immersion: 



1-545 >.^> 1-543 • 



The specific gravity := about 2.65 and the mean réfringence i = about 

 1.544 correspond to an oligoclase of the composition about Ab^Ani- The 

 calculation from the figures in the analysis has given oligoclase Ab^Ani. 



1 I take this opportunity of tendering to Miss Johnson, assistant of the mineralogical insti- 

 tution, mv best thanks. 



