28 BULLETIN 149, UNITED STATES NATIONAL MUSEUM 



Many of the enstatite chondrules are beautifully perfect spheres 

 and others oval and elongated. They occur also m all stages of frag- 

 mentation as described in the numerous publications. Irregular 

 porphyritic forms occur; such the author regards as fragmental forms 

 due to trituration and designated as "chondroids." Many stones, 

 like those of Mezo Madaras, Russia; Selma, Alabama; and Cedar, 

 Texas (pi. 18), are made up in almost their entirety of chondrules and 

 chondritic fragments, the "chondrulites" of Chamberlin.^* (See fur- 

 ther under Chondrule, its Nature and Origin, p. 29.) 



From stones of this type there is a constant gradation to the 

 crystalline chondrites of which the stones of Bluff, Estacado, or Hen- 

 derson ville may serve for purposes of illustration. These are compact, 

 dense stones showing a polished surface thickly studded with gray 

 chondrules of a few millimeters in diameter which are sharply differ- 

 entiated from the ground, sometimes breaking with it and sometimes 

 falling away leaving the surface studded with little saucer-shaped 

 pits. Some of the chondrules are of the radiating enstatite type; 

 others barred and porphyritic. The groundmass consists of a closely 

 intergrown aggregate of olivines and pyroxenes interspersed with 

 metallic particles and granules of iron sulphide. Under as high a 

 power as the thickness of the section will permit the use, the inter- 

 stitial matter polarizes faintly and shows a granular to fibrous struc- 

 ture. As a whole the structure is not that of minerals crystallizing 

 freely from a molten magma but is suggestive of a partial recrystalli- 

 zation of fine detrital material as seen in many metamorphic schists 

 (pi. 19). 



Continual variations of this are found in the same and other types 

 of chondritic stones, but it is to be noted that as the stones partake 

 more and more of the nature of crystalline rocks the included chon- 

 drules grow less and less perfect, merging finally into the groundmass 

 until they quite disappear. 



The dark color of the so-called black chondrites as shown by 

 Meunier " and subsequently by the present writer ^^ is due mainly 

 to heating though it may be in some cases in part to the presence of 

 carbonaceous matter. The coloring material in some cases is inter- 

 stitial, or again where the heating has been prolonged penetrating the 

 cleavage and fracture lines of the silicates. In the case of the stone 

 of Sevrukof, Russia, the heat has been sufficient to produce a partial 

 fusion now manifested by the presence of a little interstitial brownish 

 glass." Daubree, as quoted by Eberhard,^^ thought this heating 



« The Two Solar Families. 



» Comptes Rendus, vol. 6, p. 178. 



M Proc. Nat. Acad. Set., vol. 4, 1918, pp. 178-180. 



!' The writer will here say that he has never found in any meteorite what he considered an original, re- 

 sidual glass such as is characteristic of many terrestrial igneous rocks. Such glass as may exist is secondary, 

 as in the case above. This, of course, does not apply to other chondrules, which are often more or less 

 vitreous. 



«8 Arch. f. d. Naturkiinde Liv. Est. u. Kurlands, ser. 1, vol. 9, 1882. 



