COMPOSITION AND STRUCTURE OF METEORITES 43 



In like manner the groundmass of the Hendersonville stone is 

 described as not at all that of minerals crystallizing freely from a 

 molten magma, but suggestive, rather, of a partial recrystallization of 

 fine detrital material as seen in metamorphic schists.®'' Instances 

 in which the direct action of heat alone is more evident is afforded by 

 Figure 1, Plate 24, which is that of a chondrule in the stone of Parnallee, 

 India. That the chondrule is foreign to the ground in which it is 

 embedded is obvious. The present interest in it lies in the dark, 

 glassy border by which it is surrounded and which is considered due 

 to the action of heat on the fine, dust-lil^e material in which it was 

 embedded. That it is not an original residual glass should be evident 

 to any petrographer. 



An equall}^ instructive illustration of heat action is shown in the 

 transformation of a normal plagioclase feldspar into the mineral 

 maskelynite, as first noted b}'' Tschermak and since verified by others. 

 This is considered by the writers as indicative of a reelevation of 

 temperature sufficient to change its character even if not completely 

 fuse it, and, on sudden cooling, leave it in the form of a feldspathic 

 glass. As stated elsewhere, the mineral is not always isotropic but 

 shows frequent transition stages to the normal mineral. In the Mocs 

 meteorite the feldspar occurs, according to Tschermak, as plagioclase 

 in the mass of the stone and as maskelynite in the crust. 



The possibility of a refusion and crystallization of the feldspar 

 without the formation of maskel5mite has been showTi by the writer 

 in the case of the Estherville meteorite which is regarded as a meta- 

 morphosed agglomerate, the finer portions of which (fig. 2, pi. 2) 

 show a structure not unlike that of some partially altered crystalline 

 schists in which the feldspars fluxed without altering the fragmental 

 structure of the pyroxenes. A striking feature of this meteorite which 

 has not before been mentioned is the presence in it of boulderlike 

 masses of a different structural nature than the mass of the material 

 (pi. 13). It is to be noted that while around the border the silicate 

 material seems to merge into the general ground of the main mass, 

 the interior while evidently of the same mineral nature is of a more 

 regular texture and the metal is in very fine threads which at times 

 completely surround, or enfold the silicate particles as is often the 

 case in ordinary chondritic stones. The percentage amount of metal, 

 it should be said, is plainly much less than in the main mass. The 

 question arises. Is the nodule a pebble or a portion of the original 

 ground of the agglomerate which has escaped the metamorphic changes 

 of the rest of the mass? In either case the metamorphic nature of the 

 meteorite seems fully substantiated. LacroLx ®^ has noted the recrys- 



e" Merrill: Proc. U.S.Nat.Mus., vol. 32, 1907, p. 80. 



»9 Archiv. du mus. d'hist. Nat., ser. 6, vol. 1, 1926, p. 35. 



59587—30 4 



