SCIENCE 



NEW YORK, JULY 8, 1893. 



DIAMONDS IN METEORITES. 



BY OLIVER WHIPPLE HUNTINGTON. 



The mineral cabinet of Harvard College received some 

 time ago, through the liberality of Francis Bartlett, Esq., 

 one of the two large masses of meteoric iron first brought by 

 Dr. A. E. Foote from Arizona, and called by him the Caiion 

 Diablo iron. This mass of iron, weighing 154 pounds, is in 

 many ways unique, and chiefly so for the circumstance that 

 it contains diamonds. 



This fact was first made known by Professor G. A. Koenig 

 of Philadelphia, who found in cutting one of the fragments 

 that the cutting tool refused to penetrate the wall of a small 

 cavity which it chanced to encounter, and this cavity was 

 found to contain small black diamonds.^ One white dia- 

 mond of microscopic dimensions was said to have been 

 found but subsequently lost, and no further account of this 

 interesting occurrence appears to have been published. 



In order to determine whether other portions of the Canon 

 Diablo iron contained diamonds, the author dissolved a mass 

 of about one hundred grams weight in acid, assisted by a 

 battery. The iron was supported on a perforated platinum 

 cone hung in a platinum bowl filled with acid, and the cone 

 was made the positive pole and the dish the negative pole of 

 a Bunsen cell. When the iron had disappeared, there was 

 left on the cone a large amount of a black slime. This was 

 repeatedly washed and the heavier particles collected. This 

 residue examined under a microscope showed black and 

 white particles, the black particles being mainly soft amor- 

 phous carbon, while the composition of the white particles 

 appeared less easy to determine, though when rubbed over a 

 watch-glass certain grains readily scratched the surface. 



The material was then digested over a steam-bath for 

 many hours with strong hydrofluoric acid, and some of the 

 white particles disappeared, showing them to have been 

 silicious. Most of them, however, resisted the action of the 

 acid. These last were carefully separated by hand, and ap- 

 peared to the eye like a quantity of fine, white, beach sand, 

 and under the microscope they were transparent and of a 

 hrilliant lustre. A single particle was then mounted in a 

 point of metallic lead, and when drawn across a watch-crystal 

 it gave out the familiar singing noise so characteristic of a 

 glass-cutter's tool, and with the same result, namely, of actually 

 cutting the glass completely through. To verify the phe- 

 nomenon, successive particles were used for the purpose, and 

 with the same result. The experiment was then tried on a 

 topaz, and the same little mineral point was found to scratch 

 topaz almost as readily as it did glass. It was finally ap- 

 plied to a polished sapphire, and readily scratched that also, 

 proving beyond question that this residue of small, white, 

 transparent grains must be diamond, though no well-formed 

 crystals could be recognized. 



It has long been known that carbon segregates from mete- 

 oric iron in the form of fine-grained graphite; and, when 

 ' American Journal ot Science, Vol. xlii., November, 1891. 



Haidinger found in the Arva iron a cubic form of graphite, 

 it was suggested by Rose that the crystals might be pseudo- 

 morphs of graphite after diamond. More recently Fletcher 

 described a cubic form of graphite from the Youngdegin 

 meteorite, under the name of Cliftonite.^ 



Finally, a meteoric stone which was seen to fall at Nowo- 

 Urei, in Russia, in 1886, was discovered two years later to 

 contain one per cent of a carbonaceous material, which not 

 only had the crystalline form of the diamond but also its 

 hardness, so that, instead of being regarded as a pseudomorph 

 after diamond, it was compared with the black diamonds of 

 Brazil, called "carbonado.'" And, lastly, in the Canon Diablo 

 iron we have true diamonds, though of minute dimensions. 

 Thus it would appear that, under certain conditions, metallic 

 iron is the matrix of the diamond. 



Now, we further know that when cast iron is slowly cooled 

 a considerable portion of the carbon separates in the condi- 

 tion of graphite. Moreover, the high specific gravity of the 

 earth as a whole, as compared with the materials which 

 compose its crust, give us ground for the theory that the in- 

 terior of our planet may be a mass of molten iron. There- 

 fore it would seem to be not an unreasonable hypothesis, 

 that diamonds may have been separated from this molten 

 metal during the formation of the earth's crust; and a sup- 

 port for this hypothesis may be found in the fact that at the 

 Kimberley mines of South Africa diamonds occur in, what 

 appear to be, volcanic vents, filled with the products of the 

 decomposition of intrusive material thrown up from great 

 depths. 



The late Professor H. Carvill Lewis, in examining the 

 materials from the greatest depths of the South African 

 mines, came to the conclusion that the diamonds were formed 

 by the action of the intrusive material on the carbonaceous 

 shale there found, and on this ground predicted the discovery 

 of diamonds in meteorites;' but it must be remembered that 

 a similar geological phenomenon appears on a grand scale in 

 Greenland, and no diamonds have as yet been found in the 

 Greenland irons, though they have been so carefully studied 

 by the late Professor J. Lawrence Smith and others. 



It is difficult to conceive of any chemical reaction by which 

 diamonds could be formed from the action of melted igneous 

 rock on coal, and all attempts to prepare diamonds artificially 

 by similar means have signally failed. 



The writer would urge that the segregation of carbon 

 from molten iron is a well-known phenomenon, and the as- 

 sociation of diamonds with amorphous carbon in the meteor- 

 ite from Arizona indicates that under certain conditions such 

 a segregation may take the form of diamond. The chief of 

 these conditions is doubtless the length of time attending 

 the crystallization, though it may also be affected by press- 

 ure; and if the earth, as many believe, is simply a large iron 

 meteorite covered with a crust, it seems perfectly possible 

 that if we could go deep enough below the surface we should 

 find diamonds in great abundance. 



• Min. Mag., 7, 121, 1887. 



' American Journal of Science, xxvL, p. 74. 



* British Association, 1886, p. 667. 

 Ibid, 1887, p. 720. 



