4 BULLETIN 149, UNITED STATES NATIONAL MUSEUM 



meteorites, und need no further mention liere other than that they 

 occur as small, usually microscopic disseminated crystals and crys- 

 talline grains. Whether or not chromium enters into the composition 

 of the pyroxenes, as in terrestrial rocks, has not, as yet, been 

 determined. 



Cohenite.— This mineral was first described by Weinschenk in 

 1889, having previously been mistaken for schreibersite, which it 

 closely resembles and with which it is very commonly associated. 

 It differs, however, in being soluble in copper ammonium chloride 

 and practically infusible. It occurs in blebs and tabular masses 

 belonging to the isometric system. Chemically it is an iron carbide, 

 of the formula (FeNiCo)3C. Actual analyses of material from the 

 Canon Diablo (I) and Magura (II) irons yielded the results given 

 below : 



« Recalculated after deducting 4.68 per cent schreibersite. 

 ' Recalculated after deducting 0.65 per cent schreibersite. 



Dauhreelite. — In 1876 J. Lawrence Smith gave this name to a 

 black, lustrous, highly crystalline material found by him associated 

 with the troilite in the meteoric irons of Coahuila, Mexico. Incom- 

 plete analyses made at the time showed 36.48 per cent of sulphur, 

 some 1 per cent of iron, and a little carbonaceous matter, the unde- 

 termined portion being chromium. The true composition he an- 

 nounced as being, probably, sulphur 37.62 per cent; chromium 62.38 

 per cent.'' Later he was able to isolate the material in larger quantity 

 and greater degree of purity from the Coahuila iron, and in 1878,^ he 

 published new analyses and descriptions showing the mineral to have 

 the probable composition: Sulphur, 44.29 per cent; chromium, 36.33 

 per cent; iron, 19.38 per cent; or the formula FeS Cr2 S3. Actual 

 analyses, however, showed: Sulphur, 42.69 per cent; chromium, 

 35.91 per cent; iron, 20.10 per cent; total 98.70 per cent. 



Feldspars and maskelynite. — From what is known regarding terres- 

 trial basic igneous rocks, the feldspars of meteorites would naturally 

 be assumed to belong to the more basic varieties, as labradorite and 

 anorthite (fig. 2, pi. 2). Not many actual and complete analyses 

 are available owing to its rare occurrence and the consequent diffi- 

 culty of securing a sufficient quantity of material in a fair degree of 

 purity. Those quoted below show that in at least two instances the 



' Amer. Jour. Sol., vol. 12, 1876, p. 109. 

 « Idem, vol. 16, 1878, p. 270. 



