1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 163 



barred form somewhat resembling Fig. 9. Fig. 4 is a portion of a 

 large, clear, colorless crystal, while in Fig. 5 I have endeavored to 

 show the outlines of a fragment in which the colorless portions rep- 

 resent perfectly clear olivines imperfectly secreted from an amorphous 

 glass base so thoroughly impregnated with dust like particles as to be 

 of a deep gray or blue- black color. 



The Enstatite. — This, like the olivine, occurs both in the form of 

 chondri and as scattered fragments in the groundmass. It is distin- 

 guishable from the olivine by its gray color, less transparency, well- 

 developed cleavage parallel to the vertical axis, and by its insolubility 

 in acids. The position of the plane of the optic axes could not be made 

 out with certainty with the instrument at command, but as the mineral is 

 biaxial, non-pleochroic and extinguishes always parallel with the vertical 

 axis, there is apparently no doubt as to its true nature. The chondri 

 are sometimes composed wholly of enstatites with small quantities of 

 interstitial amorphous base, or of olivine and enstatite together. 



The distinction between the two minerals is, owing to their small 

 size and imperfect development, often impossible by the microscope 

 alone. A more common form of the enstatite is that of irregular frag- 

 ments with a radiating or fan-shaped structure, as shown in the upper 

 left portion of Fig. 1, the large lower central area in Fig. 2 and in 

 Fig. 6. Other quite perfectly spherical, very minute forms occur, con- 

 sisting of an almost wholly amorphous material or with only faint be- 

 ginnings of crystallization shown by rays of light radiating across the 

 surface as the stage is revolved. The exact mineralogical nature of 

 these can not be determined. 



The metallic iron occurs in lumps, as shown in Figs. 1 and 2, and in 

 very irregularly-outlined areas, as in Fig. 10, or as injected drops in the 

 interior of the chondri. It is of a silvery white color by reflected light, 

 and readily distinguished from the pyrrhotite with which it is nearly 

 always associated, and which shows a bronze-yellow luster. In a few 

 instances grains or chondri of olivine or enstatite are entirely surrounded 

 by a dark border of iron and pyrrhotite, as Tschermak* has figured 

 from sections of the Cabarras meteorite. In such cases the iron often 

 penetrates slightly into the mass of the mineral, having evidently exer- 

 cised a corrosive action. 



The groundmass. — The structural features of the groundmass are 

 as already observed, very obscure. It consists of minute angular parti- 

 cles of olivine and enstatite imbedded in a matrix so fine aud so badly 

 stained by iron oxides that its true nature can not be satisfactorily as- 

 certained. From the fact that this coloring matter has become so thor- 

 oughly disseminated throughout the whole mass, I am inclined to re- 

 gard it as tufaceous. A wholly granular, glassy, or partially devitrified 

 base would seemingly have proven less pervious and shown the ferru- 

 ginous staining only along lines of fracture and cleavage. Nevertheless, 



* Op. cit., Plate xix, Fig. 2. 



