88 PE0F. J. H. L. VOGT ON LABEADOEITE-NOEITE [May I909, 



Composition op the Ground-mass Minerals. 



1 Titcmo- 

 magnetite. 



Plagio- 

 clase. 



Biotite. 



1 



SiO-2 



TiOo 



A1 2 3 



Fe 2 O a ...' 



55-30 



5-29 



28-29 



62-03 



38 



2 

 17 



7 



5 

 21 



"i-s 



8-5 



52-3 49-1 

 0-8 0-8 

 2-2 2-6 

 1-1 2-2 



FeO 



MgO 



CaO 



Na 2 C 



K 2 



32-68 



10-45 

 4-95 

 1-01 



16-7 



24-0 



2-9 



14-2 

 11-1 



20-0 



- 





Totals ... 



10000 100-00 



10000 



100-00 100-00 



The composition of the ground-mass of No. 4 

 approximately as follows : — 



calculated 





9 percent. 



61-88p.c. 



3 p.c. 



13 p. c. 



13 p. c. 



0-12 p.c. 



Total- 



Total 

 found. 





Titano- 



Plagio- 



Bio- 



Hyper- 



Dial- 



Apa- 



calcu- 





magnetite. 



clase. 



tite. 



sthenic. 



lage. 



tite. 



lated. 



Si0 2 ... 





34-22 



1-14 



6-80 



6-38 





48-54 



4,7-75 \ 



TiOo ... 



0-48 





0-06 



o-io 



o-io 





( 0-74) 



1-74 



AI0O3... 





17-51 



0-51 



0-29 



0-34 





18-65 



18-71 



Fe 2 3 ... 



5-58 





0-21 



0-14 



0-29 





6-22 



6-08 



FeO ... 



2-94 





0-15 



2-17 



1-85 





7-11 



7-11 



MgO ... 







0-63 



3-12 



1-44 





5-19 



5-32 



CaO ... 





6-47 





0-38 



2-60 



0-07 



9-52 



9-47 



Na*0... 





3-06 



0-05 









3-11 



2-70 



K 2 ... 





0-62 



0-26 









0-88 



1-20 



P 2 5 ... 













0-05 



0-05 



0-05 



Totals... 



9-00 



61-88 



3-01 



13-00 



13-00 



0-12 



100-01 



100-13 



The concordance betweeu 'calculated' and 'found' is sufficiently 

 close to show that errors of any importance are practically 

 impossible. 1 



To simplify matters, I calculate the components RAl o Si0 6 , 

 BFe 2 Si0 6 , and also Ca(Fe,Mg)Si 2 G in hypersthene and (Fe,~Mg) 2 

 Si 2 O e in diallage only as respectively FeA.ljSi0 6 , FeFe„SiO G , CaFe 

 Si s 6 , and Fe 2 Si 2 6 . In reality there may he besides these also 

 some MgAl 2 SiO (i ," MgFe 2 SiO e , CaMgSi 2 6 , and Mg 2 Si 3 O e ; this is, 

 however, not taken into consideration either here or further on. 



1 It may be remarked, however, that the small quantity of titanium-oxide 

 in the ferromagnesian silicates is perhaps estimated a little too low, and the- 

 eilica correspondingly a little too high. 



