168 REPORT OF NATIONAL MUSEUM, 1899. 



L. DE LA UNA Y. Les Diamants du Cap. 



ORVILLB A. 'DERBY. Brazilian Evidence on the Genesis of the Diamond. 



The Journal of Geology, VI, 1898, p. 121. 

 H. W. FCRMISS. Carbons in Brazil. U. S. Consular Reports, 1898, p. 604. See also 



Engineering and Mining Journal, LXVI, 1898, p. 608. 

 M. J. KLINCKB. Gites Diamantiferes de la Republique sud-Africaine. 



Annales des Mines, XIV, 1898, p. 563. 



GRAPHITE. Graphite, plumbago, or black lead, as it is variously 

 called, is a dark steel gray to black lustrous mineral with a black 

 streak; hardness of but 1.2, and a specific gravity of from 2.25 to 2.27. 

 The prevailing form of the mineral is scaly or broadly foliated (Speci- 

 men No. 51007, U. S. N. M.), with a bright luster, but it is sometimes 

 quite massive (Specimen No. 61138, U. S. N. M.) and columnar (Speci- 

 men No. 59976, U.S.N.M.) or earthy, with a dull coal-like luster 

 (Specimens Nos. 64795 and 63133, U.S.N.M.). 



Its most characteristic features are its softness, greasy feeling, and 

 property of soiling everything with which it conies in contact. 

 Molybdenite, the sulphide of molybdenum, is the only mineral with 

 which it is likely to become confounded. This last, however, though 

 very similar in general appearance, gives a streak with a slight green- 

 ish tinge, and when fused with soda before the blowpipe yields a sul- 

 phur reaction. Chemically, graphite is nearly pure carbon. The 

 name black lead is therefore erroneous and misleading, but has become 

 too firmly established to be easily eradicated. 



The analyses given below show the composition of some of the purest 

 natural graphites. 



As mined the material is almost invariably contaminated by mechan- 

 ically admixed impurities. Thus the Canadian material (Specimens 

 Nos. 59977, 62153, U.S.N.M.) as mined yields from 22.38 to 30.51 

 per cent of graphite; the best Bavarian, 53.80 per cent (Specimen No. 

 52050, U.S.N.M.). The grade of ore that can be economically worked 

 naturally depends upon the character of the impurities and the extent 

 and accessibility of the deposit. It is said 1 that deposits at Ticonde- 

 roga, New York, have been worked in which there was but 6 per cent 

 of graphite (Specimen No. 37825, U. S. N. M.). 



Occurrence and origin, Graphite occurs mainly in the older crystal- 

 1 Engineering and Mining Journal, LXV, 1898, p. 256. 



