402 G. r. MERRILL ON METAMORPHISM IN METEORITES 



Further, they are almost universally characterized by the presence of 

 the colorless, sometimes isotropic, maskelynite, the calcium phosphate 

 merrillite, and an occasional enwrapping and interstitial smoky glass, as 

 in the Parnallee stone. It is among stones of these groups, also, that 

 Berwerth, to whom we are indebted for the most satisfactory suggestions 

 on the subject, found his "N^etzbroncit" structure and such secondary 

 changes as were to him indicative of meteoric metamorphism. 



Causes of Variation in Structure 



The question may well be asked if the variations noted are original or 

 due to metamorphism. In his paper on the Zavid stone,^^ Berwerth, it 

 will be recalled, described the interstices of the porphyritic olivines occu- 

 pied by a "platyfibrous" form of bronzite ("Netzbroncif) which enacts 

 structurally the role of the metal in a pallasite. 



In a second paper he considers this with especial reference to meta- 

 morphism and draws the conclusion that this ^'Netzbroncit'' is a sec- 

 ondary product due to a jjartial fusion and hasty recrystallization of the 

 finer bronzite material in a chondritic tuff. The shattered condition of 

 the individual constituents producing the cataclase structure so charac- 

 teristic of meteorites of this class he considers due to this same reheating 

 and sudden cooling process. With these conclusions the present writer 

 takes no' exceptions other than to state that he is unable to discover in 

 slides of the white and gray chondrites at his disposal the netzbroncit 

 structures developed to the extent and degree of perfection figured by 

 Berwerth in his description of the Zavid stone, excepting in the porphy- 

 ritic chondrules themselves, as noted above, and, further, he believes the 

 cataclase structure to be due in part, at least, to crushing. 



Moreover, he feels that there are other easily recognized criteria of 

 metamorphism, mentioned below, of equal diagnostic value. I refer to 

 the almost universal presence in the stones of these groups of the anom- 

 alous feldspar or feldspathic glass maskelynite and the equally anomalous 

 calcium phosphate merrillite (figures 3 and 4, plate 3). 



The name maskelynite, it will be recalled, was first given by 

 Tschermak^'^ to an isotropic constituent of the habit and composition of 

 a labradorite feldspar occurring in the stone of Shergotty. The name 

 has siuce been extended to cover a colorless interstitial substance, some- 

 times quite isotropic and sometimes faintly doubly refracting, of like 



1'' Wissenscliaft. Mltthoil. aus Bosnien u. der Hei-segovina, vol. 8, 1901. See. also. 

 "Uber die Structure des cliondritischen Meteorsteln. Central, fiir Min., etc., 1901, pp. 

 641-647. 



" Sitzbericht der k. Akad. der Wiss., vol. 65, February, 1872, p. 127. 



