186 DESCRIPTIVE MINERALOGY. 



GRAPHITE. 



[From the Greek ypoiptj, I write; in allusion to its use.] 



Graphite. Haay and Ckaveland. — Plumbago or Graphite. Tliomson. — Plumbago. PhiMps and Shepard. — 

 Rhombohedral Graphite. Jameson. — Rhomboedrischer Melan-Graphit. Mohs. 



Fig- 16- Description. Colour dark steel grey, inclining to iron black. 



Streak black. It occurs crystallized in regular six-sided tables (Fig. 

 16); also in granular concretions, massive and disseminated. Pri- 

 mary form a rhombohedron, the dimensions of which are unknown. 

 Cleavage perfect, perpendicular to the axis. Fracture uneven, con- 

 choidal and slaty. Lustre metallic. Opaque. Sectile. Hardness 

 from 1 .0 to 2.0. Specific gravity from 2.08 to 2.45. It is infusible 

 by the blow-pipe ; but in a high degree of heat, it is combustible, 

 ^ and leaves a residuum of oxide of iron. 



Composition. Graphite was for a long time considered as a compound of graphite and 

 iron ; but it is now thought that the iron, the proportion of which is very variable, and seldom 

 exceeds ten or eleven per cent., is entirely accidental. The mineral may be regarded as 

 carbon, differing only from the diamond, charcoal, etc., in the mode of aggregation of its 

 ultimate particles. 



Geological Situation. This mineral is almost always found in primitive rocks, usually 

 granite or white limestone. In the State of New- York, the latter is the more common matrix, 

 although veins of considerable extent are also found in granite. 



Uses. Graphite has long been employed in the manufacture of lead pencils and crayons. 

 It is also used for making crucibles and portable furnaces, for giving a gloss to the surface of 

 iron, and for counteracting friction between rubbing surfaces of wood or metal. 



localities. 



In another part of this work (page 96), I have noticed our principal localities of graphite. 

 A few others may here be added ; and to avoid repetition, it may be stated that the white 

 limestone, wherever it occurs, usually contains scales or imperfect tabular crystals of this 

 mineral. The finest specimens of this kind have heretofore been found in the vicinity of Port 

 Henry in Essex county, and in the town of Monroe in the county of Orange. Very fine spe- 

 cimens, having a six-sided form, and exhibiting distinct rhombohedral cleavages, have been 

 found by Dr. Emmons at Johnsburgh in Warren county. But graphite, when it occurs in 

 this manner, is seldom in quantities which render it valuable for economical purposes. 



Columbia County. Mr. Mather informs us that graphite is common in the talcose and 

 talco-argillaceous rocks of the Williamstown range ; in Hancock mountain, east of New- 

 Lebanon ; and east of Hillsdale. Two miles east of the latter a bed has been opened, which 



