GRAPHITE 301 



The mineral occurs in two forms, the crv^stalHne imd the 

 amorphous. Crystalline graphite is usually found in a com- 

 pact foliated or granular mass. At times the crystals are in 

 the form of distinct hexagonal plates. The amorphous variety 

 is, as its name implies, without crystalline structure, The term 

 has been used to include a wide range of natural carbo- 

 naceous products — such as the graphitic anthractie of Rhode 

 Island, which is of a structure between scaly and granular, 

 and selected samples of which contain as much as 52 per 

 cent of carl)on; and the so-called Baraga graphite of Michi- 

 gan, which in reality is a carbonaceous schist. The crystalline 

 variety consists of finer grades, and hence is used where soft- 

 ness and a smooth uniformity of structure are desirable, as 

 for lubricants or in the better grades of pencils. Graphite is 

 iron black or steel gray in color and has a metallic luster; 

 to the touch it is smooth and soap like. Its specific gravity 

 varies from 2.015 to 2.583, the variation being due to the 

 impurities — such as iron oxide, alumina, magnesia, lime, 

 and silica — which are present in all natural graphite. Usually, 

 there is also from five tenths of 1 per cent to 1.3 per cent 

 of hydrogen — a fact which seems to point to an organic origin. 

 Graphite is infusible, and resists the corrosive action of many 

 chemicals and molten metals. These properties render the 

 crystalline variet}^, with its flake like form, of great value 

 in the manufacture of graphite crucibles for special purposes — 

 for instance, to resist intense heat in the manufacture of 

 crucible steel; to possess great density at a high heat, as in 

 the refining of gold and silver; and to resist the corrosive 

 action of easily oxidized metals and alloj^s in a molten con- 

 dition, as in melting brass, bronze, etc. Although cr^'stalline 

 graphite will burn in ox}'gen at and above a temperature of 

 575° C., it is a good conductor of heat and electricity; this 

 property renders it of special value for the manufacture of 

 the commutator brushes used in electrical machines, for use 

 in electroplating, and for electrodes in many electrolytic 

 chemical processes. 



In its chemical relations, graphite occupies a position 

 distinct from that of any other form of carbon. The most 

 striking difference is the effect of treatment with fuming nitric 



