22 BULLETIN 149, UNITED STATES NATIONAL MUSEUM 



when etched. The silicates in the Crab Orchard meteorite were ad- 

 judged on chemical grounds to be enstatite and anorthite.^^ Vaca 

 Muerta and Hainholz are in so close agreement as to need no further 

 notice here. 



Thin sections of the stony portions of the Morristown mesosiderite 

 show it to be holocrystaliine granular, sometimes strongly cataclastic. 

 The latter structure is particularly conspicuous in those portions rich 

 in metallic iron, where the feldspars are often enclosed in the form of 

 sharply angular fragments in the iron or in its numerous embay- 

 ments. The appearance is not, however, that of a clastic rock, but 

 rather that of a crystalline mass which has been subjected to dynamic 

 agencies. The structure as a whole is quite irregular, and sometimes 

 porphyritic through the presence of large pyroxenic masses which may 

 be 5 to 8 mm. in diameter. 



The groundmass of the stone is composed mainly of granules of 

 pyroxenes and plagioclase of such size as to render their determination 

 a matter of considerable ease, but which are interspersed with in- 

 numerable roimded and irregular granular forms so minute and so 

 lacking in crystal outlines as to obscure their true mineralogical nature. 



The feldspars are in angular fragments showing polysynthetic 

 twinning and numerous cavities and enclosures. Partial analyses on 

 a minute quantity indicate it to be anorthite. A very small amount 

 of olivine is present. 



The remarkable meteorite of Estherville, Iowa, is, however, as noted 

 above, of a different type, though how far this difference is original, 

 and how far due to metamorphism remains yet to be shown. The 

 stone has been the subject of much discussion, a general summary of 

 which, up to 1915, is given by Farrington.*^ As shown in Plate 13 it 

 consists of disconnected and irregular blebs of metal distributed 

 throughout the silicates and often with irregular cavities intervening. 

 The silicate components are enstatite, diallage, olivine and anorthite. 

 The enstatite occurs in two forms, a green and highly lustrous variety 

 and a yellow-brown opalescent fdled with minute glass cavities. It is 

 to the last that Smith gave the name "peckhamite." Subsequent 

 studies " have shown this to be but an altered phase of the green 

 mineral, a change evidently brought about through the agency of heat. 

 Both the pyroxenes and olivine occur at times in globular pebblelike 

 forms. The groundmass is holocrystaliine anorthite, often showing 

 signs of incipient fusions and other indications of metamorphism. 

 (See p. 40). 



Pallasites. — Meteorites of this group — with the exception of 

 Brezina's rokickites — differ in that the prevailing silicate (olivine) 

 occurs in such forms as to seemingly show its crystal development 



« Amer. Journ. Sci., vol. 34, 1887, p. 387. 



« Mem. Nat. Acad. Sciences, vol. 13. 



*' Proc. U. S. Nat. Mus., vol. 58. pp. 363-370. 



