6 MEMOIRS NATIONAL ACADEMY OF SCIENCES. [vol.xiv. 



Mc Kinney, Collin County, Tex. — It is remarkable that this interesting stone, which has 

 been known since 1895, should have been allowed so long to remain unstudied, the bibhography 

 consisting only of a brief statement by von Hauer ' regarding the acquisition by the Vienna 

 museimx of upward of 40 kilograms of the material, a description of the stone by Brezina,' 

 based evidently only on an examination by the naked eye, aided perhaps by a pocket lens, a 

 brief note by Meimier ^ calling attention to the evidence it afforded of the introduction of the 

 metal and sulphide after consolidation, and lastly an analysis by Whitfield given in my paper 

 on the minor constituents of meteorites* the last named made with particular reference to the 

 possible occurrence of bariima, strontixmi, zirconium, or other of the rare elements. 



Macroscopically the stone is fine-grainetl, compact, dull brownish gray, almost black, 

 looking on a broken surface very much like a piece of hard shale, shoAving here and there a minute 

 fleok of metal, and with chondrules quite inconspicuous except where it is polished. The 

 texture is firm and the chondmles break with the stone. On the polished surface they are of 

 greenish color, suggestive of a sei-pentinous alteration, which, however, microscopic examina- 

 tion shows not to have taken place. 



In the thin section the microscope reveals, in addition to the iron and iron sulphide, three 

 varieties of pyroxene, one occurring in broad plates ^vith wide (25°-30°) extinction angles, a 

 polysyntheticaUy twinned variety and normal enstatite, in addition to olivine and the calcimn 

 phosphate, while the whole mass is here and there so impregnated with a coal black compound 

 as to give it the dark color referred to. 



The chondrules are varied and interestiug. They consist of enstatite ia the common 

 radiating and cryptocrystaUine forms as well as in good, weU developed phenocrysts in a glassy 

 or fibrous base. Sometimes the entire chondrule is composed of small, closely compacted 

 forms -mth httle or no interstitial base. Others are formed wholly of the polysj-nthetically 

 twinned monocUnic forms. These twinned pyroxenes occur also scattered throughout the 

 groundmass and under such condition with relation to their associated minerals as to suggest 

 a dynamic action, a crowding and crushing, and sometimes even raising the question if the twin 

 structure may not itself be due to this same cause. The occurrence of the twioned forms in 

 the chondmles where there are no signs of strain forbids, however, the universal apphcation of 

 any such theory of origin. Still other chondrules are wholly of oUvine. The calcium phosphate 

 occurs in the usual irregular, interstitial, colorless forms with low relief. The groimdmass 

 is everj'where so obscured by the black matter that it is impossible to make out a structure for 

 a certainty. It is apparently fragmental, though if we accept Meimier's views, it may have 

 been caused by the reheating to which he ascribes this black color. In this connection Brezina 

 says "Dessen Zugehorigkeit zu den Cs insofeme nicht ganz sichergestellt ist, als die schwarze 

 Farbe nicht mit Bestimmtheit auf einen Kohlegehalt Zuruckgefuhrt ist". (See further imder 

 "Effects of dry heat on meteoric stones," Proc. Nat. Acad. Sci., vol. 4, 1918, p. 178.) 



This black constituent, which is s\ifficiently abimdant to give the stone a imiform color, 

 is by no means imiformly distributed, but, as shown in the thin section and figures, is injected 

 throughout the groimd and along cleavage and fracture lines of the various minerals, being 

 absent in quantity from the chondrules, forming a dense black, opaque groimd from which 

 these and the scattered, often fragmental sQicates stand out sharply. An attempt was made 

 to determine the possible presence of a hydrocarbon, but the facilities at command did not 

 enable me to arrive at a satisfactory result. One hundred grams of the pulverized stone were 

 digested for 48 hours, first in ether and next in carbon disulphide. Although care was taken 

 to use the purest chemicals obtainable, and the filters were fii'st washed in ether, the slight, 

 colorless extract obtained in the first instance, and the single small drop of a greenish, oil- 

 like matter in the second, were both felt to be perhaps in part due to impm-ities. Any hydro- 

 carbon, if present at all, is certainly there in very small quantities. The apparent introduction 

 (or perhaps better •production) of the coloring matter at a late period in the history of the 



' Ann Hof-Mus., vol. 10, 1895, p. 34. ' Revision des Pierres Mcteorique, etc., p. 412. 



> Idem, pp. 252, 253. * Mem. Nat. Acad. Sci., vol. 14, 1916, p. 19. 



