18 AMERICAN MUSEUM GUIDE LEAFLETS 



as graphite (cliftonite) and as hydrocarbons. Diamonds were first 

 found in Canyon Diablo in 1891. They are extremely minute in size 

 but recognizable crystals have been obtained. Graphite (cliftonite) 

 occurs usually in nodules and only in siderites in particles that are large 

 enough for easy examination. The material is very fine. The cliftonite 

 form of graphite is considered by most authorities to be a pseudomorph 

 after diamond. 



Hydrocarbons of several kinds have been found in meteorites. Ac- 

 cording to Cohen 1 they may be grouped into three classes: (1) compounds 

 of carbon and hydrogen alone; (2) compounds of carbon, hydrogen and 

 oxygen; (3) compounds of carbon, hydrogen and sulphur. None of 

 the meteorites in the Foyer collection is known to contain any hydro- 

 carbon, but the fact that any meteorite should contain such substances 

 is of great scientific interest. It is pretty clear that they belong to the 

 pre-terrestrial history of the masses; hence, since they are readily com- 

 bustible or volatile, the meteorites that contain them cannot have been 

 heated to high temperatures, at any rate, subsequent to the formation 

 of the compounds. This is an additional argument in support of the 

 statement already made that the heating of meteorites during aerial 

 flight is, in many instances at least, only superficial. Furthermore, the 

 existence of hydrocarbon compounds in meteorites, where no life can 

 have existed, shows that organisms are not absolutely necessary to the 

 formation of such compounds in the earth's crust. 



Cohenite, which is a carbide of iron, nickel and cobalt, is tin-white 

 in color and looks like schreibersite. It is much rarer, however, and 

 occurs in isolated crystals. The only terrestrial occurrence of cohenite 

 is in the basaltic iron of (Jreenland. Moissanite, the natural carbide 

 of aluminum corresponding to the artificial carborundum, has thus far 

 been found only in Canyon Diablo, where it occurs in microscopic 

 crystals. It is the latest discovery among the constituents of meteorites, 

 having been found in 1905 by Henri Moissan. 



As far as investigations have been carried, heating develops the fact 

 that meteorites contain gases condensed within them, either by occlusion 

 in the same way that platinum and zinc absorb hydrogen or by some 

 form of chemical union. According to Cohen'-' the following gases have 



' Meteoritenkunde. Heft I, p. 159. 

 2 .Meteoritenkunde. Heft I, p. 169 



