THE CONSTITUENTS OF METEORITES 523 



but has been detected in several and in the Coahuila irons occurs 

 in nodules of considerable size (i7'"™X 12°^™). 



It is identical with terrestrial chromite in composition and 

 properties. Not being acted upon by acids, it may be readily 

 distinguished from daubreelite. It is generally non-magnetic, 

 but sometimes feebly magnetic. Where crystals occur they are 

 commonly octahedrons, sometimes modified by other forms. 



Amorphous carbon. — Meteorites of the group known as car- 

 bonaceous meteorites, as well as some others, are permeated by 

 a dull-black pulverulent coloring matter which is usually left as 

 a residue on treatment of the meteorite with acid. This residue 

 sometimes amounts to from 2-4.5 P^^ cent, of the mass. 



A residue similar in character though smaller in amount is 

 likewise found after dissolving many of the iron meteorites. 

 These residues on being heated in air glow, usually become 

 lighter in color and give off carbon dioxide. They must there- 

 fore be considered practically pure carbon. 



Berzelius and Wohler believed this carbon to have originated 

 so far as the carbonaceous meteorites are concerned, from the 

 decomposition of the hydrocarbons of the latter. In this respect 

 they regarded it analogous to terrestrial humus, though of very 

 different origin. Smith considered it similar in origin to the 

 graphite of iron meteorites and Weinschenk believes it similar to 

 one of the forms of carbon produced in the making of cast iron. 

 No indications that it had an organic origin have ever been dis- 

 covered. 



Diamo7id. — The existence of diamonds has been definitely 

 proven in only two meteorites, those of Canon Diablo and Nowo- 

 Urei. Diamonds have, however, also been reported from the 

 irons of Magura and Smithville and the stone of Carcote. The 

 diamonds of the Caiion Diablo meteorites have been most 

 studied. Here they are found as minute particles or dust left 

 as a residue after dissolving the meteorite in acid. The particles 

 rarely exceed ^ ^^ in diameter. They are usually brown to 

 black in color but sometimes are colorless and transparent. 

 They accompany graphite, amorphous carbon and often troilite 



