2 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.64, 



other are concave, and each is characterized by smaller concavities 

 or pits; the surfaces of the three faces being formed of a smooth 

 black skinlike coating. The other faces are lighter in color (dark 

 gray), several of which are only slightly concave, and all are essen- 

 tially free from pits or minor concavities. Examination of the stone, 

 especially the lighter-colored portion, clearly shows it to be tuff- 

 aceous in texture, which is pronounced in thin section under the 

 microscope. 



Thin sections under the microscope show the stone to be a crystal- 

 line spherulitic chondrite composed chiefly of olivine and enstatite 

 and a considerable sprinkling of metallic iron. Plate 1, Figure 1, 

 a composite photograph of the sawn surface of the stone, emphasizes 

 in the right half the metallic portion shown in the tiny bright white 

 spots, and in the left half, taken with the light at a different angle^ 

 the rock or silicate portion. 



Microscopically, thin sections of the stone show it to be composed 

 of chondrules of olivine and enstatite set in a dark brown ground- 

 mass composed of a mixture of particles of metallic iron and small 

 fragments of the silicate minerals (pi. 2, figs. 1 and 2). The exact 

 nature of the groundmass is largely obscured in most of the thin 

 sections studied, due to the general presence of iron oxide stain de- 

 rived from oxidation, which also frequently partially discolors the 

 chondrules and large fragments of silicates. However, treatment of 

 a thin section of the stone with dilute hydrochloric acid to remove 

 the stain of iron oxide clearly shows the composition of the ground- 

 mass to be a mixture of metallic iron and small fragments of the 

 silicate minerals olivine and enstatite. The general structure of the 

 stone, which is characteristically tuffaceous, is shown in Figures 

 1 and 2 of Plate 2. 



The metallic iron forms small particles of irregular shapes dis- 

 tributed through the groundmass as interstitial filling between the 

 chondrules, as tiny particles inclosed in the chondrules, and occa- 

 sionally as minute granular films between the fibers of the enstatite 

 chondrules which show radiate structure. It sometimes forms par- 

 tial rims or borders about the chondrules. 



Chondrules of several types occur as shown in Figures 1 and 2 of 

 Plate 2. They vary from holocrystalline to those composed of part 

 glass and porphyritic, the outlines of which are usually sharply dif- 

 ferentiated from the matrix. Some are of the radiate enstatite type 

 which may show an excrescence or saucer-shaped depression (pi. 

 2, fig. 1) , but most of them are of the glass porphyritic type composed 

 either of olivine or of a mixture of olivine and enstatite in a glass 

 base (pi. 2, fig. 2). An occasional barred form composed of olivine 

 occurs. Plate 2, Figure 1, shows two large chondrules of the radiate 

 enstatite type which, under cross nicols, exhibit pronounced cone- 

 shaped extinction. 



