No. 4.) 



RESEARCHES ON METEORITES— AfERRILL. 



13 



embeckled in a crystalline ground of the same constituents, and the metallic components. Where 

 not stained by oxidation the silicates are beautifully clear and pellucid . The pyroxene is in part 

 of the normal enstatite type, though many of the larger forms are monodinic, showing extinction 

 angles as high as 25°. In almost the first section examined attention was attracted to a minute, 

 irregular, colorless area traversed by numerous fracture lines, with only moderate rehef, non- 

 pleochroic, and polarized in faint bluish-gray colors. Its appearance at once suggested the 

 phosphatic mineral described by me in a previous paper.' Microscopic examination of a con- 

 siderable number of slides, accompanied in some instances by microchemical tests, showed the 

 mineral to be a calciiun phosphate, and occurring not infrequently. In no instance was the 

 mineral found in the crystalline form characteristic of apatite. Nearly altogether it occurs as 

 an interstitial filling, almost isotropic, and, as in the previous cases which I have described, of 

 lower refractive indices than normal apatite. Indeed, in many instances the mode of occurrence 

 and low relief without cleavage or crystal outline causes it to resemble on casual inspection an 

 interstitial glass, for which doubtless it has heretofore been frequently mistaken. In such cases, 

 it is onl}' by treating a sUde with a drop of acid and watching the mineral gradually disappear, 

 then testing the solution, that its true nature can be determined. 



Further examination showed the presence of this phosphate in the Waconda stone where 

 it could not be recognized even microscopically. It was found that when the surface of an 

 micovered slide was treated with a dilute solution of hydrochloric acid and allowed to stand 

 for not more than a quarter of an hour, the solution thus obtained would react for phosphorus 

 and calcium, and the slide when examined be found to contain frequent minute, irregular, 

 interstitial pits where the material had been dissolved away. 



These determinations natujaUy suggested the possible phosphatic nature of the white 

 spots before noted. An examination with a pocket lens showed these to be composed of aggre- 

 gates of minute crystals of a faint yellow-green tint. It being obviously impossible to rely 

 on cutting a thin section including the desired area, recourse was made once more to micro- 

 chemical tests on minute fragments broken out by a needle point. Reactions for phosphorus 

 and calcium were easily obtained, the mineral being readily soluble in cold nitric acid and less 

 so in hydrochloric acid. Dr. E. S. Larsen kindly determined the indices of refraction by solu- 

 tions, as follows: a =1.627 ±0.003; 7= 1.621 ±0.003. These results are low for normal apatite, 

 agreeing more closely with those obtained by Dr. Wright on material from the Alfianello and 

 Rich Mountain stones, as given in the paper before referred to. 



As phosphorus was not determined by J. L. Smith in his analysis of either the metallic 

 or silicate portions of this stone, a second analysis was decided upon. The results as deter- 

 mined by Dr. J. E. Whitfield are given below, Smith's results being also given for purposes of 

 comparison. 



Preliminary separations yielded: 



> On the montlceUite-Uke mineral in meteorites, and on oldhamite as a meteoric constituent, Froc. Nat. Acad. Sci., voL 1, 1915, p. 302, and On 

 the calcium phosphate o( meteoric stones, Amer. Joum. ScL, vol. 43, 1917, p. 322. 

 < Not determined. 



