298 



Field Columbian Museum — Geology, Vol. I. 



although it has not infrequently been reported by other analysts as a 

 constituent of the soluble portion of meteorites. 



Grouping the compounds of the above analysis which are known 

 to enter into the composition of nickel-iron, chrysolite and bronzite, 

 the following may be deduced as the probable composition of these 

 three ingredients : 



COMPOSITION OF NICKEL-IRON. 



Fe 

 Ni. 

 Co. 



Per Cent. 



78.65 



20.26 



I .09 



IOO.OO 



COMPOSITION OF SOLUBLE SILICATES (CHIEFLY CHRYSOLITE). 



Per Cent. 



Si0 2 



MgO 

 FeO 

 A1 2 0. 

 Cr 2 0, 

 CaO ' 



36.88 



36.40 



18.62 



6.64 



1.38 



0.08 



Ratio of 2RO:Si0 2 : : 1.9997 : 1. 



COMPOSITION OF INSOLUBLE SILICATES (CHIEFLY BRONZITE AND 



MONOCLINIC PYROXENES). 



Per Cent. 



Si0 2 56.52 



A1 2 3 3.07 



FeO ' 6.05 



MgO 29.28 



CaO 2.94 



CoO . . .0.10 



NiO ■ 1.45 



Na 2 0.53 



K.,0 0.06 



100.00 



Ratio of RO : Si0 2 : : 1:1.0148. 



To place the alkalies in the pyroxenes, as is here done, is con- 

 trary to the usual custom, it being common to assume that they are 

 present as feldspars. But as no feldspars could be detected in the 

 slides and as alkalies are known to enter into the composition of 

 pyroxenes in small amount, the conclusion here adopted seems the 

 more reasonable one. No attempt was made to differentiate the two 

 pyroxenes chemically, as I know of no guide for this. The amount 

 of monoclinic pyroxene which can be seen in sections is very small, 



