HOVEY, THE FOYER .METEORITES 19 



been found: hydrogen, carbon dioxide, carbon monoxide, nitrogen and 

 marsh gas (light carburetted hydrogen). 



Troilite is common in meteorites and constitutes brass- or bronze- 

 yellow nodules, plates and rods which are to be seen in nearly every 

 section, particularly of siderites. The mineral is usually considered to 

 be the simple sulphide of iron, FeS, but its exact chemical composition 

 and crystalline structure are still matters of investigation and dispute. 

 Canyon Diablo and Willamette contain, or contained, much troilite 

 in the shape of rods, and the fusion and dissipation of this mineral during 

 the aerial flight of the masses gave rise to some of the holes which pene- 

 trate them, and the same statement is true of many other meteorites. 

 Pyrrhotite, the magnetic sulphide of iron, Fe H S 12 , occurs in stone 

 meteorites and chiefly in the form of grains. Daubreelite is likewise 

 a sulphide of iron, but it differs from those just mentioned through con- 

 taining much chromium, giving the chemical formula FeS, Cr 2 S 3 . The 

 mineral is peculiar to siderites and siderolites and has never been found 

 in the stone meteorites or in the earth's crust. It occurs in Canyon 

 Diablo, where it may be seen surrounding nodules of troilite as a black 

 shell with metallic luster. 



Oldhamite, a sulphide of calcium, CaS; tridymite, a form of silica, 

 SiO,; chromite, an oxide of iron and chromium, FeCr 2 4 ; magnetite, 

 the magnetic oxide of iron, Fe 3 4 ; osbornite, another sulphide or 

 oxysulphide of calcium, and lawrencite a chloride of iron, Fe Cl 2 , occur 

 sparingly in some meteorites. Lawrencite manifests itself rather dis- 

 agreeably through alteration to the ferric chloride, which oozes out of 

 the masses of iron and stands in acrid yellow drops on the surface or runs 

 in streaks to the bottom. Glass like the volcanic glass of terrestrial 

 rocks seems never to be absent from the interior of stone meteorites, 

 but from the nature of the case it is not found in iron meteorites. 



Surface Characferistics. 



The surface of a newly-fallen meteorite always consists of a thin 

 veneer or crust which differs in marked degree from the interior of the 

 mass. In the case of the siderites, this seems to be a polish due to melt- 

 ing and friction, together with partial oxidation. Some iron meteorites 

 which are known to have lain long in the ground likewise show a crust 

 which is somewhat similar in appearance, but it is due to slow oxidation 



