26 BULLETIN 149, UNITED STATES NATIONAL MUSEUM 



stone described by Borgstrom " the fragments are more angular, the 

 stone partaking of the nature of a breccia (pi. 17). 



Fully 90 per cent of the stony meteorites are characterized by the 

 presence of small spherical bodies embedded in a fragmental or crys- 

 talline ground of the same mineral nature. Mineralogically speaking, 

 the bodies are of pyroxene or olivine, rarely feldspar, though some- 

 times glassy and without the development of determinable mineral 

 species. In sizes they vary from too small to be visible to the unaided 

 eye to rarely a centimeter in diameter. These are called chondrules 

 from a Greek word meaning a grain and are of exceptional interest on 

 account of their unique form and probable origin. A discussion of 

 these features must, however, be left until later. 



The chondritic meteorites, or chondrites, as they are called, form a 

 group quite variable in types of structure as shown in the several 

 plates here devoted to the subject. They are at times so friable as 

 to crumble easily in the thumb and fingers, or again are very hard 

 and tough, this feature being imparted by metamorphism. In the 

 first instance the chondrules may fall away entire. In the second they 

 may be so firmly embedded as to break with the matrix. All inter- 

 mediate stages occur. A description of the internal structure — the 

 manner in which the various minerals are disposed relative to one 

 another in a chondritic meteorite — is a matter of no small difficulty. 

 As a whole, the group may be said to consist of a heterogeneous aggre- 

 gate of minerals largely olivine and pyroxenes, mainly in a fragmental 

 condition, with varying amounts of interstitial metal and metallic 

 sulphides throughout which the chondrules are scattered in varying 

 proportions. It is only when we consider the crystalline chondrites 

 that a satisfactory verbal description can be given. 



The chondrites are described by Wiilfing (Meteoriten in Samm- 

 lungen, pp. 449-454) as magnesia-rich stones consisting essentially of 

 ohvine, bronzite, nickel iron, and iron sulphide, and with the excep- 

 tion of Novo-Urei plainly chondritic and tuffaceous. The}^ are 

 divided into : 



1. Howarditic chondrites, comprising transition members from the 

 howardites into the true chondrites. 



2. White chondrites, yellowish white tuffaceous stones with chon- 

 drules for the most part of the same color. 



3. Intermediate chondrites, transition forms into the gray chondrites. 



4. Gray chondrites, yellowish to blue gray tuffaceous stones with 

 variously colored chondrules firmly embedded in the ground mass. 



5. BlacJc chondrites, firm, dark gray to black stones in which the 

 color is due in part to carbonaceous matter and in part to pyrrhotite. 

 The chondrules are mostly of a lighter color. Meunier has shown 

 that in some instances the blackening has been produced by heat. 



"Bull. Com. Qeologique de Finland, No. 34, 1912. 



