250 AimUAL REPORT SMITHSONIAN INSTITUTION,, 1942 



ponent to the percentage of iron in the meteorite. The points on the 

 graph represent the specific meteorites listed in table 4. There is a 

 grouping of points in the lower left-hand portion of the graph. 

 Points Ch,* So, and En are rather well grouped, as are also points 

 La, Te, Lu, and Pe ; the other seven are so widely dispersed that it is 

 useless to attempt a serious discussion of a curve based on these data. 

 A straight-line relationship would not necessarily be expected in 

 plotting values on this graph, and a curve drawn at some later time 

 when more data are available would probably be found to flatten 

 out toward the right-hand side of the figure. 



It is evident that this series of stony meteorites offers little proof 

 of any progressive increase in the percentage of nickel in the iron 

 as the quantity of iron decreases in the meteorite. Table 4, however, 

 shows some of the ranges of indices of the different types of irons 

 and indicates that in the metal of stony meteorites an even greater 

 range in the cobalt-nickel to iron ratio exists. 



Before leaving the idea of the correlation between abundance of 

 metal in a stony meteorite and its cobalt-nickel content, mention 

 should be made of a further suggestion, namely, that as the cobalt- 

 nickel to iron ratio gets lower there is a related progressive change 

 in the ratios of FeO : MgO in the silicates. The Soko Banja and 

 Chicora meteorites contain a very small percentage of metal, but 

 what is present is exceedingly rich in cobalt and nickel — ^hence the 

 ratio index is rather low. The bulk of the silicates in each of these 

 meteorites is olivine and pyroxene, and both of these silicates are 

 rich in FeO. Again many meteorites have been found to contain con- 

 siderable percentages of metallic inclusions in contact with the 

 magnesium silicate enstatite, which has been found to be about the 

 purest enstatite known — almost without a trace of iron. 



From what can be observed by examining sections of stony meteor- 

 ites, it is difficult to see how there could be any relationship between 

 the composition of the metallic portions and the composition of 

 the silicate minerals. Judging from the physical relationship of 

 the iron to the other minerals present, it would appear that the metal 

 solidified later than the silicate minerals. A chondrule is shown in 

 plate 6 completely surrounded by a ring of metal, and such features 

 as these are not uncommon. Merrill ^ called attention to the thread- 

 like forms of iron penetrating silicates, and it is difficult to see how 

 these delicate threads could enter a silicate mineral unless the iron 

 solidified in the fractures of previously formed minerals. 



A convincing array of evidence can be offered to show that chon- 

 dritic meteorites are tuffs — that is, they represent a type of rock 



* The first two letters of the meteorite names are used to designate the position on the 

 graph. 



» Proc. U. S. Nat. Mus., vol. 73, art. 21, 1928. 



