OBSERVATIONS OF LUMINOUS METEORS. 363 



could be distinguished. The first is a clear greenish mineral, with in- 

 complete cleavage along two directions perpendicular to each other, and 

 identified as olivine. A second in round tough spherules, brownish in 

 hue and not numerous, with a finely foliated or finely fibrous structure, 

 was found to be bronzite. Enclosed particles are sometimes made up of 

 these two minerals, sometimes, but not very frequently, of them together 

 with a third silicate in long greenish prisms which have the appearance 

 and angles of augite. The meteorite also contains some magnetic pyrites 

 (troilite ?), a very little nickel-iron and perhaps a little carbon, to which 

 the dark hue of the matrix is due. 



Tschermak directs attention to two peculiarities observed in several 

 chondritic meteorites, and noticeable in this one. The first is the occur- 

 rence of a crust over the surface of the bronzite spherules, possessing 

 fibrous structure. This crust is thin, and is distinguished from the 

 enclosed material by its paler colour ; it has the same fibrous structure, 

 doubly refractive power, and, in fact, is optically orientated like the en- 

 closed silicate. It appears to be produced by some agent acting from 

 without, perhaps heat in conjunction with a reducing gas. The agent 

 has not caused fusion, but a slight modification of the texture of the sur- 

 face. The second point which he has observed is the distribution in zones 

 of the magnetic pyrites in many of the granular enclosed masses. When 

 a microscopic section is examined by reflected light, it is found that many 

 are apparently surrounded by a crust of the metallic sulphide, in others 

 it occupies the centre of the mass in all cases apparently filling up inter- 

 stices. It seems as if the sulphide had impregnated the rocky mass, and 

 the absence of all magnetic pyrites in the very compact enclosed particles 

 and the tough fibrous bronzite chondra, confirms this view. This im- 

 pregnation Tschermak believes took place after the enclosed mineral 

 particles attained their present form, and the only explanation which can 

 be suggested is that this must have happened while the whole tufacious 

 mass was strongly heated. According to this theory, the enclosed granules 

 coming in contact with fused magnetic pyrites must have drawn it into 

 the fine fissures and interstices, in some instances into the cavities of 

 the granules themselves. 



This argues the existence of two definite stages in the formation of 

 these and similar chondritic structures. First, the production of the 

 olivinous tuff by the splitting and attrition of the rock when the tougher 

 particles are rolled and rubbed together till they have a roundish or 

 spherular form ; and secondly, a subsequent application of heat to the 

 tuff, accompanied not unfrequently by the reducing action of gases 

 and vapours. 



The Grosnaja meteorite appears to consist of — 



Silicic acid 33-78 



Alumina 3-44 



Iron protoxide 28-86 



Lime 3-22 



Magnesia 23-55 



Potash 0-30 



Soda 0-63 



Carbon 0-68 



Hydrogen 01 7 



Magnetic pyrites 5-37 



100-00 



