18 BULLETIN 18 4, UNITED STATES NATIONIAL MUSEUM 



Troilite is easily recognized by its bronze-yellow, brassy, or 

 brownish color, its low hardness (4), and the readiness with which 

 it is attacked by acids, which produce an odor of hydrogen sulphide. 

 It may also be identified by a sulphur print, as explained in chapter 

 XVII. It is nonmagnetic and its streak is black. It does not 

 reduce copper from solutions of copper salts. 



In composition troilite is substantially identical with terrestrial 

 pyrrhotite, though the composition of the latter is FeiiSi2, while 

 that of troilite is probably FeS. Troilite is not found in terrestrial 

 rocks. 



Troilite crystals. — Until recently troilite had rarely been found 

 to show a definite crystalline form. Rose found imperfect micro- 

 scopic crystals in a stony meteorite, from which he determined that 

 its crystallization is hexagonal, and similar minute crystals with 

 measurable angles were found by other investigators (Meunier, 

 1884; Cohen, 1894, p. 190). 



A well-developed macroscopic crystal was found by the author 

 in Seneca Township (1939), and shortly afterward Nininger (1939) 

 described similar fairly well defined macroscopic crystals in Monahans. 

 More recently the author found relatively large microscopic crystals 

 of great perfection and beauty in Otumpa (pi. 48). 



Daubreelite. — Daubreelite, discovered by Smith in 1876 in Coa- 

 huila, and later observed in many irons, is an iron-chromium sul- 

 phide not found in terrestrial rocks. Its composition is FeS-Cr2S3. 



It is commonest in hexahedrites, much less common in other 

 irons. It usually is associated with troilite, adjoining or bordering 

 it, or intergrown with it. Not infrequently it crosses the troilite 

 in parallel bands (pi. 48). 



Daubreelite is black or dark brown, has a black streak, is very 

 brittle and not magnetic. Unlike troilite, it is said not to be attacked 

 by hydrochloric acid, though dissolved by nitric acid. Under the 

 microscope it is likely to show a chipped or broken surface because 

 of its brittleness. Where bands of troilite and daubreeUte alternate, 

 the former appears darker in color. 



Its crystallization is not kno^vn, but it tends to assume quad- 

 rangular forms. 



Schreibersite. — The most interesting accessory constituent of 

 meteoric irons is the iron-nickel phosphide sclireibersite, both because 

 of its peculiar and varied forms and because of its important metal- 

 lographic aspects. It appears in many forms, illustrated in the 

 plates — as small microscopic crystals in the shape of squares, rhombs 

 and short quadrangular baguettes, termed rhabdites; as needles, 

 sometimes stout and again exceedingly fine and long; as lamellae 

 or elongated bodies scattered along the boundaries of octahedral 



