COMPOSITION OF METEORITES. 



945 



The above data give the approximate composition of the lithosphere as 

 now constituted; but not of the earth as a whole. As pointed out by Far- 

 rington," we can probably get a rough approximation to the composition of 

 the earth by considering the nature of meteoric falls, as they are supposed to 

 furnish the best basis for estimating- the composition of the material out of 

 which the world has segregated. Meteoric falls rather than meteoric finds 

 are chosen because "the iron meteorites' are much more likely to be known 

 and preserved than the stony." 6 The average specific gravity of meteoric 

 falls, as determined by Farrington, is 3.69." No attempt has been made to 

 estimate quantitatively the proportions of the elements which compose such 

 meteorites, taking into account both their masses and compositions. How- 

 ever, Farrington'* recently considered the mineral and chemical compositions 

 of various classes of meteorites, including both falls and finds, and in some 

 cases gave the relative proportions of a few of the elements in these, and 

 the percentages of a few of the minerals in some of the meteorites con- 

 sidered. From his article the following table is made: 



Constituents of meteorites. 



Relative proportions. 



Percentage of total of 

 definite meteorites. 



Chrysolite 



Orthc-rhombic pyroxenes. 



Monoclinic pyroxenes: 

 Augite 



Diopside 



Plagioclase: 



Anorthite ... 



Albite 



Oligoclase. .. 



Labradorite . 

 Maskelynite 



ESSENTIAL. 



ndFe 



(MgFe) : Si0 4 



All gradations between: 

 MgSi0 3 (enstatite) 

 (MgFe)Si0 3 (bronzite) 

 ( FeMg) Si0 3 ( hypersthene ) 



Ca(MgFe)(Si0 3 ) 2 



with (MgFe)(AlFe) 2 SiO 



|CaMg(Si0 3 )» 



(Ca(MgFe)(Si0 3 )o 



CaAl.Si»0 8 



NaAlSi 3 O s 

 Ab G Ani to Ab 3 Anj 

 AbAn (1:1 or 1:3) 

 About same as labradorite . 



Per cent. 

 Ni 6-20 

 (Co .5-2) 

 (Cu .006-.02) 

 Fe 10-30 

 Ni almost lacking. 



35 (2 meteorites). 



22.5 (1 meteorite). 



« Farrington, 0. C, The average specific gravity of meteorites: Jour. Geol., vol. 5, 1897, pp. 127-128. 

 & Farrington, The constituents of meteorites: Jour. Geol., vol. 9, 1901, p. 394. 

 '"Farrington, The average specific gravity of meteorites: Jour. Geol., vol. 5, 1897, p. 130. 

 d Farrington, The constituents of meteorites: Jour. Geol., vol. 9, 1901, pp. 393-408, 522-532. 



MON XLVII — 04 60 



