COMPOSITION AND STRUCTURE OF METEORITES 31 



origin of these peculiar bodies. In other words, there has been a 

 failure to recognize or discriminate between the kugelchen with 

 radiate structure and the often polysomatic forms with the irregular 

 fracture. 



The follo^\dng pages represent an attempt on the part of the author 

 to make this discrimination and to show how far proposed theories 

 may apply to the various forms presented. 



At the outset and for the purpose of making clear what is to follow, 

 it will be well to figure and describe a few characteristic forms of the 

 individual chondrules. This notwithstanding the previous most excel- 

 lent and comprehensive work of Tschermak and Cohen.^^ (See pis. 

 18, 22-25.) 



Mineralogically, the chondrules, using the word in its broadest 

 and most comprehensive sense, in nearly all meteorites are composed 

 chiefly of the minerals olivine or pyroxene, the latter in either ortho- 

 rhombic or monoclinic forms, or both. Some are largely of an 

 undifferentiated glass. Feldspars occur but rarely except in the form 

 known as maskelynite. In addition are occasional inclosures of metal 

 or metallic sulphides, chromite or other minor constituents. The 

 metallic iron sometimes occurs in rounded chondritelike blebs, 

 though it is doubtful if this should be referred to under that name. 

 Structurally, the chondrules in the same meteorite may vary from 

 densely cryptocrystalline, almost amorphous, to those that are part 

 glassy and porphyritic or even holocrystalline. 



1. Glassy, cryptocrystalline, and radiated forms. — In Figures 1 and 2, 

 Plate 22, are shown examples of cryptocrystalline forms from the 

 stones of Barratta, Australia, and Cullison, Kans. That of Figure 1 

 is of a peculiar brownish translucency and very dense, resembling 

 the "felsitic" structure of the early petrologist. In the Cullison 

 stone. Figure 2, the chondrules, also of a brownish color, are not com- 

 pletely isotropic but between crossed nicols break up into several ill 

 defined areas over which the dark cloud sweeps faintly and irregularly 

 as the stage revolves. The material seems to be a partially de vitrified 

 glass in a condition of optical stress as from sudden cooling. Chon- 

 drules of this type and those next to be described more nearly resemble 

 the spherulites of the terrestrial rocks than any others which have 

 come under the writer's notice. Their outlines are at times as sharply 

 demarked from the matrix in which they are embedded as are the 

 spherulites in the rhyolitic obsidians of the Yellowstone National 

 Park. 



Chondrules of the radiating type are shown in Figures 3, 4, and 5, 

 from the meteorites of Elm Creek, Hessle, and Parnallee. The 

 mineral in all cases is enstatite ^^ and the outline of the spherule as 



«3 See particularly, Die Mikroscopbische BeschafEenheit der Meteoritenkunde, respectively. 

 ^ No attempt in these pages has been made to distinguish between enstatite and the ferruginous varieties 

 bronzite and hypersthene. 



