THE STRUCTURE OF METEORITES 53 



Matter of meteorites of two kinds.— Matter constituting meteor- 

 ites may be described as of two kinds, metallic and stony. The 

 metallic matter is chiefly an alloy of iron and nickel, the stony 

 matter chiefly the silicates chrysolite, pyroxene, and feldspar. 

 Single meteoric masses may consist of but one of these kinds of 

 matter or may be made up of a union of the two. 



Three groups of meteorites according to their components. — 

 According to the relative quantities of each of the two above men- 

 tioned kinds of matter it is convenient to divide all meteorites 

 into three great groups. Those made up wholly or largely of metal 

 [aerosiderites, holosiderites) form the first group. Those made up 

 of about equal quantities of metal and stone [aerosiderolites, 

 lit/iosiderites, sj/ssiderites) form the second group. Those made 

 up wholly or largely of stone [aerolites, sporadosiderites) form 

 the third group. No sharp dividing line can be drawn between 

 these groups. They pass into one another by every gradation, 

 and meteorites of the two kinds even occur in the same fall. 

 Yet meteorites of these groups differ in many essential char- 

 acters and their separation becomes a matter of great conve- 

 nience in study. For purposes of the present study the three 

 classes will be sufficiently designated by the terms iron meteor- 

 ites, iron-stone meteorites, and stone meteorites. 



Two groups of meteorites according to their origin. — With 

 respect to their origin meteorites may be either ( I ) monogenic 

 (of single origin) or (2) polygenic (of various origin). Most 

 of the iron meteorites are plainly monogenic. Many show such 

 homogeneity and uniformity of structure as could belong only 

 to a single crystal. Thus the iron meteorite of La Caille, a 

 mass of 591 kilos in weight, contains inclusions of troilite 

 arranged in parallel rows throughout in such a manner as to indi- 

 cate a uniform and continuous crystallization of the entire mass. 

 Likewise from a mass of a Toluca meteorite a cube may be cut 

 which shows on etching a perfectly regular octahedral structure 

 throughout. The same parallelism of planes may be traced 

 on an etched section of almost any of the so-called cubic meteo- 

 rites, such as Coahuila, Hex River, etc. A few iron meteorites 



