ON THE MINERAL COMPOSITION AND STRUCTURE OF 

 THE TROUP METEORITE. 



By George P. Merrill. 



Head Curator of Geology, United Stales National Museum. 



The general megascopic character of this stone has been sufficiently 

 described in Prof. J. A. Udden's paper. 1 The chondritic structure is 

 quite indistinct and might at first seem doubtful but for the occa- 

 sional presence of larger forms (2 to 3 mm. in diameter) of a white 

 and gray color. The texture is firm and the chondrules break with 

 the matrix. The amount of metal (3.1 per cent) given in Doctor 

 Schoch's analysis (p. 475) is much smaller than one would be led to 

 suppose from the appearance of a polished surface (see pi. 1 01 of Pro- 

 fessor Udden's paper), and the writer ventures to suggest that the 

 small amount of material ("some 2 or 3 grams") utilized did not cor- 

 rectly represent the character of the stone as a whole. This has in 

 the past been an altogether too frequent cause of error by those who 

 have regarded meteorites as too precious for exhaustive study. 



In thin sections under the microscope the stone presents an 

 extremely variable, granular, and indistinctly chondritic structure, 

 such as is characteristic of many of the intermediate chondrites, to 

 which group this stone is assigned. So extremely variable is it as 

 to almost baffle description (pi. 102). Areas of closely interlock- 

 ing olivines and enstatites in crystalline granules of considerable 

 size give way abruptly to those showing large irregular outlined 

 fragmental material surrounded by narrow zones so finely granular 

 as to give only aggregate polarization, and these again to imperfect 

 chondroidal forms, sometimes porphyritic and sometimes of barred 

 or radiate structure. Throughout the entire mass and within the 

 chondrules themselves abundant irregular clear and transparent, 

 almost completely isotropic areas of glass (maskelynite), with 

 interstitial areas of colorless calcium phosphate (merrillite) are by 

 no means rare. Indeed, so abundant are the last named that it 



i Proc. U. S. Nat. Mus., vol. 59, 1921, pp. 471-476. 



Proceedings U. S. National Museum. Vol. 59-No. 2384. 



477 



