8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



at the temperature of measurement. The resulting bulk density figures 

 of 2.330 for the Georgia tektite and 2.332 for the Martha's Vineyard 

 tektite agree within the limit of error of the measurement (estimated 

 to be 0.002 g./cm. 3 ). These density figures are slightly lower than 

 the lowest specific gravity figure (2.334) given by Barnes (1940) 

 for bediasites and are in the middle of the range of density figures 

 (2.303 to 2.367 g./cm. 3 ) he gives for moldavites. Conversion of 

 Barnes's specific-gravity values to densities is not possible because of 

 insufficient data. The difference between our values and his lowest 



Table 2. — Comparison of physical properties of the Martha's Vineyard and 



Georgia tektites 



Martha's Vineyard 

 Georgia tektite tektite 



Property (USNM 1396) (USNM 2082) 



Color Light olive green Light olive green 



Weight (g.) ii.4 a i7-76 b 



Index of refraction i.485±0.003 c i.4852±o.ooo4 d 



Density (g./cm. 3 ) 2.330 2.332 



Magnetic susceptibility (e.m.u./g.) . . 3.6X10-*' 3.90X10"" 



Magnetization o* o* 



■ Remaining portion of specimen. 



b Complete specimen. 



c Determined by I. Friedman, U. S. Geological Survey. 



d Bulk index determined by E. C. T. Chao, U. S. Geological Survey. 



• From Senftle and Thorpe (1959). 



f Determined by A. Thorpe, U. S. Geological Survey. 



bediasite value could be more apparent than real. The close agree- 

 ment of density values for the two specimens under study combined 

 with their chemical compositions (table 4) confirms the impression 

 obtained from transparent sections that bubble size and distribution 

 in the two materials are the same. 



The index of refraction of both the Martha's Vineyard and Georgia 

 tektites is 1.485. This value is slightly less than the smallest value 

 (N N a=i-488) given by Barnes (1940) for bediasites and in the mid- 

 dle of the range (N Na = 14798 to 1.4961) he gives for moldavites. 

 Barnes (1940, pp. 522-523) has used the Gladstone and Dale rela- 

 tionship to plot index of refraction and density data to show relation- 

 ships of these data for the various tektite groups and other natural 

 glasses. The data for the Martha's Vineyard and Georgia tektites 

 give a specific refractivity of 0.208, which falls in the moldavite area 

 of Barnes's plot, outside of the area where moldavites and bediasites 

 overlap. 



Magnetic data for a number of tektites and other glasses have been 

 obtained and discussed by Senftle and Thorpe (1959). The magnetic 



