GUIDE TO THE MINERALOGIC 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 10 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 spare 

 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 l»ecn 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. .'{!>,(. 



2 Siderolites. .Masses of a Bpongy, 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. 



