ANALYSES OF KOCKS. 



599 





I. 



II. 



HI. 



IV. 



V. 



SiOa 



60.01 

 20.12 



2.82- 



58.18 



22.89 



4.58 



64.59 



19.84 



2.24 



62.27 

 21.07 



47.60 



Al.,0. 



4.66 



^\ 1-2^^6 



Fe.,0, 





FeO 





12.73 



CaO 



MgO 



K,,0 



5.15 



.23 



3.67 



6.43 



4.61 



.71 



4.17 



2.97 



1.26 



.63 



3.53 



7.88 



5.10 



""3.86" 

 6.76 



18.06 

 14.56 



Xa^O 



MnO 



1.50 

 trace. 



HP 



.77 



.96 





.81 



.50 



Specific oravitv 



99.20 

 2.559 



99.07 



99.97 





99.61 

 3.283 















I. Anorthoclase from Volcano projectiles of 1888 ; analyzed by W. F. Scoular. 

 II. Anorthoclase from the " Rhombenporphyr " of Lille Frogner; analyzed by 



Kjerulf.t 



III. Anorthoclase from the taimyrite of the Taimyr river, Siberia. i 



IV. Same as I, recalculated so as to exclude magnetite and augite impurities. 

 V, Augite from Volcano projectiles of 1888; analyzed by L. C. Urban. 



The analysis of this felspar clearly shows that it is sodium orthoclase, the com 

 position corresponding to Orj Ab.,. 55 An,. 12. The study of the sections indicates 

 that we have present both the " X^atronorthoklas " and the ' ' Xatronmikroklin " 

 of B nigger. 



The plagioclase of the phenocrysts has a more lath-shaped habit and shows the 

 albite striation. The extinction angles in the zone of the ortho-diagonal indicate 

 that the felspar is near the middle of the plagioclase series- A portion was sep- 

 arated in the Thoulet solution and partially, analyzed for me by Mr Leo C. Urban 

 with the following results : 



CaO, 



6.4i 



Na.,0. 



5.22 



K.,0.. 



1.87. 



The potash i)resent is pr()])al)ly explained by the fact that tlie anorthoclase was 

 not (luite eliminated from the i)ortiou analyzed. If correction ])e made for this the 

 mineral is seen to be an andesine of the formula Ab, An,. Besides the large plieno- 

 crysts, both anorthoclase and andesine occur in a second generation of phenocrysts 

 as well as in the groundmass, so that tliree distinct g<.merations are recognized. 



Augite, like felspar, occurs in three generations. The phenocrysts show about 

 equal development of pinacoids and prism. Both pinacoidal partings are generally 

 more or less developed, and twins, according to the usual law, are common in the 

 phenocrysts of the second generation. Fluid inclusions filling cavities of the form 

 of negative crystals are very common. The absorption is green in tones from yel- 

 lowish green to deep green or deep brownish green, indicating the presence of a 



* Total iron. ' 



t W. V. Brogger -. Die Silurisehen Et.igen, p. 205. 



J See K. V. Kroutschoff: Bull. acad. im. St. Petersburg, Melang. geol. et paleou', I, liv. 1. 



