524 STUDIES FOR STUDENTS 



and schreibersite. They have a tendency to gather in little 

 clefts or hollows and are not regularly distributed. Their char- 

 acter as diamond is proven chiefly by their hardness, but analy- 

 ses and a study of their behavior in polarized light give 

 confirmatory results. Huntington found some also which showed 

 crystal forms of diamonds. The occurrence of diamonds in 

 meteorites suggests interesting analogies with their terrestrial 

 occurrence. Knop and Daubree call attention to the fact that 

 the peridotic rocks in which terrestrial diamonds occur are the 

 rocks most nearly allied in composition to meteorites. In the 

 iron meteorites, as Moissan has proven satisfactorily by experi- 

 ment, diamond is to be considered a form in which, under certain 

 conditions of heat and pressure, carbon separates. Moissan 

 obtained diamonds by heating to a high temperature iron satu- 

 rated with carbon and allowing it to cool under pressure. The 

 carbon was then found to exist in three forms, graphite, foliated 

 carbon, and a diamond powder which latter corresponded to 

 that obtained from the Canon Diablo meteorites. 



A form of carbon resembling graphite but differing in hav- 

 ing a hardness of 2.5 and being isometric in crystallization, has 

 been noted in the Magura, Cosby's Creek, Youndegin, Toluca 

 and a few other iron meteorites. It was first discovered by 

 Fletcher, who considered it a distinct species and gave it the 

 name cliftonite. Other authorities, however, regard cliftonite 

 as a pseudomorph after diamond, since its crystals closely 

 resemble those of diamond in form. 



Daiibr^elite . — This mineral is an iron-chromium sulphide pecu- 

 liar to meteorites. Its composition is Fe S, Cr^ S3. It is found 

 in nearly all the cubic iron meteorites and has also been identi- 

 fied in the irons of Toluca, Nelson county, Cranbourne, Caiion 

 Diablo and others. It has never been found in stone meteorites. 

 It usually accompanies troilite, either bordering nodules or cross- 

 ing them in veins. Sometimes, however, it occurs as thin plates 

 or grains. It is black in color, has a black streak, is of metallic 

 luster, brittle and not magnetic. It is infusible before the blow- 

 pipe and becomes magnetic in the reducing flame. It is not 



