168 



REPORT OF NATIONAL MUSEUM, 1899. 



L. DE LAfXAY. Les Diamants du Tap. 



Paris, 1897. 

 Okvii.le a. Derby. ]>razilian Evidemv on the Genesis of the JMamond. 



The Journal of (ieology, VI, 1898, p. 121. 

 H. W. FfRMiss. Carbons in Brazil. U. 8. Consular Reports, 1898, p. 604. See also 



Engineering and Mining Journal, LX VI, 1898, p. 608. 

 M. J. Kmncke. Giles Dianiantiferes de la Republique sud-Africaine. 



Annales des Mines, XIV, 1898, p. 568. 



Graphite. — Graphite, phtiiibago, or black lead, as it i.s variously 

 called, is a dark steel gray to l)la('k lustrous mineral with a black 

 streak; hardness of but 1.2, and a specilic 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. 61795 and 63133, U.S.N.M.). 



Its most characteristic features are its softness, greas}" feeling, and 

 property of soiling everything with which it comes 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 l^efore the blowpipe yields a sul- 

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

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

 too firmly established to ()e easily eradicated. 



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

 nattiral graphites. 



As mined the material is almost invariably contaminated b}' 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 worker 

 naturally depends upon the character of the impurities and the extent 

 and accessibility <>f the deposit. It is said^ that deposits at Ticonde- 

 roga. New York, ha\e l)een worked in which there was but 6 per cent 

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



Occiirrencr and origin. — Graphite occurs mainly in the older crystal- 



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



