166 PEEIDOTITE. 



ish interstitial glass, and scattered crystals of chromite. In the next type 

 enstatite enters as a constitnent, and the chondritic structure appears. The 

 groundmass is of a grayish color sprinkled with iron, pyrrhotite, and 

 brownish ferruginous spots ; and is composed of grains and crystals of 

 olivine, enstatite, chromite, iron, and base, enclosing larger masses of these 

 minerals and chondri. The base is fibrous-granular in structure, and varies 

 from a light to a dark ash-gray, while it occurs with every gradation, from 

 that not affecting polarized light to that in which the differentiation has 

 been carried to such an extent that it shows a feeble coloration in this light, 

 and at best is only a semi-base. The chondri are composed of olivine and 

 base, enstatite and base, and enstatite, olivine, and base; all being more 

 or less associated with iron ores, and generally passing gradually into 

 the adjoining groundmass. The olivine chondri usually contain a darker 

 base than the enstatite chondri, and are composed of grains and crystals of 

 olivine cemented by the base, which in some cases produces forms some- 

 Avhat resembling organized structures (Plate II. figure 4). The enstatite 

 chondri show, like the olivine ones, a more or less spherical form. The 

 enstatite chondri are usually composed of fan-like, eccentrically radiating 

 ribs of enstatite cemented by the lighter gray fibrous base, and they 

 sometimes simulate superficially certain organized structures (Plate II. fig- 

 lu-e 6 ; Plate III. figure 1). The olivine and enstatite chondri are composed 

 of granules and crystals of enstatite and olivine cemented by the base 

 (Plate II. figure 5). 



The olivine of the meteorites is usually clear or pale greenish, although 

 often stained by ferruginous material along its fissures. It is more or 

 less fissured, contains inclusions of glass and iron ores, and generally is 

 in rounded grains, and but rarely in well-defined crystals. 



The enstatite is in grains and crystals, which are clear and transparent, 

 but which sometimes display a faint green tinge, and contain glass inclu- 

 sions. The mineral shows as a rule one longitudinal approximately parallel 

 cleavage, with sometimes another — or a cross fracture — at right angles 

 to the first cleavage (Plate III. figure 6). The iron is in irregular grains, 

 having in the section in reflected light an appearance nearly like ground 

 steel (Plate II. figures 4, 5, 6 ; Plate III. figure 3). Sometimes the iron is 

 quite dark, and is united with pyrrhotite and possibly magnetite (Plate III. 

 figures 2, 3, 4, 5, 6 ; Plate IV. figure 1). The pyrrhotite shows a dark bronze 

 color and a rough granulated surface in reflected light, and frequently sur- 



