14 BULLETIN 149, "UNITED STATES NATIONAL MUSEUM 



Table 1. — Measured and calculated angles of iron phosphide 



[Tetragonal, c=0.346 0.001] 



The fact that the mineral never occurs in good crystal form, lends 

 color to the suggestion made elsewhere ^^ to the effect that the 

 schreibersite is not a true mineral species but a solid solution of 

 rhabdite in varying proportions of nickel-iron. 



Silica. — Silica in the form of quartz was doubtfully identified by 

 Wohler in the meteoric stone of Hainholz and by Klein in that of St. 

 Marks. All doubts concerning the latter are set at rest by the find- 

 ing, by Merrill, of well-defined crystal particles as shown in Figure 3 on 

 Plate 11. It is to be noted that the crystals are imbedded in the me- 

 tallic portion. Silica in the form of tridymite (asmanite) constitutes 

 some 8.527 per cent of the pallasite of Steinbach, and Berwerth has 

 described both quartz and tridymite occurring imbedded in the augite 

 of the stones (eukrites) of Juvinas, Stannern, Jonzac, and Peramiho. 

 This he suggests may be a form of pyrometamorphism due to heat 

 when the meteor stream of which they formed a part came near the 

 sun. Nearly every detailed analysis of metallic meteorites shows 

 traces of silica, which, if reliance can be placed on the examination of 

 the "insoluble" residues of these irons, occurs in the form of crystal- 

 line granules and distinct crystals. The manner in which these 

 residues are obtained, it must be confessed, throws a doubt on some 

 of the determinations, but the occurrence of the mineral noted above 

 imbedded in the metallic portion of the St. Marks stone at least 

 insures the possibility. 



Troilite. — This name was given by Haidinger ^^ to a monosul- 

 phide of iron first found in nodular masses in the meteorite of Al- 

 bareto and since shown to be an almost universal constituent of 

 meteorites (see fig. 1, pi. 21). The theoretical composition as 

 demanded by the formula FeS, is iron (Fe) 63.64; sulphur (S) 36.36. 

 Actual analyses nearly always show traces of nickel and sometimes 

 copper. The mineral was named in honor of Domenico Troili, one 

 of the early enthusiastic defenders of the possibility of meteorite 

 falls. Meunier and some others have been inclined to regard the 

 mineral as identical with pyrrhotitc. Rose suggested the possi- 

 bility that the sulphide in stony meteorites might be in the form of 



'2 Mem. Nat. Acad. Sci., vol. 19, 1922, p. 6, footnote. 

 " Sitz. Akad. Wiss. Wien, vol. 47, 1863, p. 283. 



