GUIDE TO THE MIXERALOGIC COLLECTIONS 



131 



Brown coal or lignite. Brown coal contains more oxygen than 

 bituminous coal, is compact or earthy and yields a brownish 

 black powder. 



For a more detailed discussion of the occurrence and geologic 

 relations of coal deposits the reader is referred to New York 

 state museum bulletin 19 or to some work on economic geology. 



METEORITES 



Considerable knowledge regarding the probable character of 

 heavenly bodies other than the earth is furnished by the meteor- 

 ites or fallen stars. These fragments from planetary space 

 contain a number of minerals which are identical with terres- 

 trial species, as well as several which have not, up to this time, 

 been found on the earth. 



They have been classified into three groups: 



1 Siderites. Metallic masses composed principally of iron 

 alloyed with nickel and some manganese and cobalt. Polished 

 surfaces of siderites when etched with dilute nitric acid develop 

 a series of intersecting lines or bands which are known as Wid- 

 manstatten figures (pi. 39J. 



2 Siderolites. Masses of a spongy, cellular character composed 

 partly of iron and partly of stony material and frequently con- 

 taining embedded grains of chrysolite. 



3 Aerolites. Masses composed principally of stony material 

 in the form of silicates including chrysolite, enstatite and min- 

 erals in the pyroxene group. 



Meteorites are of universal distribution and can not be said 

 to be characteristic of any locality. 



