NO. 4 TEKTITE SPECIMENS CLARKE AND CARRON 13 



analyses in some detail to the new data. Barnes's analysis No. 5 was 

 excluded from the comparison because of its atypical ferrous to ferric 

 iron ratio and the possibility that this reflects either a peculiar oxidiz- 

 ing history for this specimen or analytical error. 



Only two of the nine moldavite analyses have a higher silica content 

 (82.3, 82.7 percent Si0 2 ) than the new analyses, and two have essen- 

 tially the same value (80.5, 80.7 percent Si0 2 ). The remaining 

 analyses range from 77.8 to 80.0 percent Si0 2 . The total iron for 

 the new analyses is within the range given for moldavites, but our 

 analyses suggest an appreciably higher proportion of Fe 2 3 (seven 

 of the moldavite analyses report only FeO). A recent moldavite 

 analysis given by Vorobbev (i960) has a total iron in the expected 

 range with a ferrous-ferric ratio similar to that obtained for the 

 Martha's Vineyard and Empire, Ga., material. Our analyses show a 

 lower proportion of CaO in the alkaline earth fraction, and the total 

 CaO + MgO is only about half of that observed for the moldavites. 

 The total alkalies are within the range given by Barnes, but the propor- 

 tion of Na 2 is considerably higher. The ratio of percent K 2 to 

 percent Na 2 is smaller on the average by a factor of slightly greater 

 than 3. These observations relating to chemical composition estab- 

 lish that the Georgia and Martha's Vineyard glasses are significantly 

 different from moldavite glass as we understand it today. 



The similarity of composition shown by our analyses seems to be 

 extended in the recent publication by Barnes (i960) of a chemical 

 analysis of a light green tektite from Fayette County, Tex. Its com- 

 position is very close to that of the Georgia and Martha's Vineyard 

 material. Minor differences are a slightly higher Si0 2 and a higher 

 proportion of Na 2 in the combined alkalies. These differences are 

 so small that they suggest a relationship between this specimen and 

 the two we have studied. Barnes (i960) also states that this material 

 contains no bubbles and is significantly different from bediasites. 



Ehmann (i960) has reported on a study of nickel-iron ratios in 

 tektites and other glasses. Neutron activation analysis was used to 

 determine accurate Ni values, and tektites were observed to have 

 Ni/Fe( X io 4 ) values ranging from 4.7 to 57, with a moldavite hav- 

 ing a value of 10. It is interesting that the value of this ratio is 9 

 for the Martha's Vineyard, Mass., and Empire, Ga., specimens calcu- 

 lated on the basis of our semiquantitative spectrographic Ni value 

 of 0.0015 percent. 



