GRAPHITE (from Gk. -ypaoh, graphs, writing, from 70.0eiv, graphein, to write), BLACK LEAn, or PLUISIBACO. A dark steel-gray to black mineral, having a black streak, hardness of 1.2, and specific gravity of 2.25 to 2.27. It crystallizes in the hexagonal system, and may occur in foliat ed form, massive, or even in hexagonal crys tals, but its greasy feel, softness, and black streak enable it to be easily distinguished. Mile black lead is the popular name, it is misleading, for graphite is nearly pure carbon, with only 1 or 2 per cent. of impurities, as can be seen from the following analyses: Although widely distributed, graphite rarely occurs alone in large deposits, but is usually mixed with other minerals, so that it requires special treatment after mining to separate it from the accompanying rock. It is usually found in crystalline metamorphic rocks, such as lime stones, gneisses, or sehists, and especially those of Pre-Cambrian age; still deposits are known to occur in the Carboniferous. It has also been found in small quantities in meteorites. Two forms of graphite are recognized, viz. the crys talline or true graphite, and the amorphous or graphitic anthracite. The deposits form veins, disseminations, or beds. On account of the chemi cal similarity to anthracite coal, many have con sidered graphite to be of organic origin, and some have taken its presence in Pre-Cambrian rocks as an indication of the existence of plant life at that time. The organic theory is correct, how ever, in only a few instances: e.g. when beds of coal are found passing into graphitic anthracite as the result of intense metamorphism in cer tain parts of the deposit. The Rhode Island and Bavarian graphite is of this nature. In vein deposits or disseminations in gneissic rocks, it is more probable that it has originally been in troduced into the rock in the form of a liquid hydrocarbon, which has subsequently been con verted into graphite; while in other cases, as in Ceylon, Weinschenk believes that the graphite is of volcanic origin, and due to the reaction be tween carbon dioxide and cyanogen compounds. In some limestones which have been subjected to contact metamorphism the carbonaceous matter has been changed to graphite.
The chief commercial sources of graphite are Ceylon and Austria-Hungary, smaller amounts being produced in Bavaria, Italy, Siberia, Mexico, Japan, Canada, and the United States. The Ceylon deposits, which are worked entirely by natives, are of great extent, and masses of solid graphite weighing several hundred pounds are sometimes found. The Canadian graphite occurs in Laurentian rocks, notably in the vicinity of Brougham, and has been obtained in lumps of large size. In the United States crystalline graphite is mined near Hague, N. Y., and to a
considerable extent in Chester County, Pa. At the former locality it occurs in a bed of quartzite inclosed between gneiss. Other localities in the United States are Alabama, Wyoming, North Carolina, Wisconsin, Michigan, and Rhode Island. That obtained from the last two localities is amorphous graphite.
Graphite is used in the manufacture of lead pencils, lubricants, stove-blacking, paint, refrac tory crucibles, and foundry facings. For pencils and lubricants the best grades have to be em ployed, and in the manufacture of crucibles, which consumes the larger part of the product, the graphite has to be mixed with clay and sand. Recently the substitution of a mixture of graph ite and grease for red lead has met with much success. Since graphite, as it occurs in nature, is always mixed with other minerals, the material after being mined is crushed, and then put through some kind of cleaning or concentration process. The separation is done either by means of an air-current or water, preferably the latter.
In 1898 the manufacture of artificial graphite from coke was begun at Niagara Falls, and in the year of its discovery 200,000 pounds of car bon rods were graphitized in the electric furnaces, while in 1900 the production had risen to 860, 750 pounds. It is said that the artificial product is fully equal to the natural material in its electrical conductivity, for use as a lubricant, and in the manufacture of stove-polish or lead pencils.
Although the production of graphite in the United States has been increasing almost every year, still the amount produced is far from sufficient to supply the domestic demand. The imports therefore continue to be large. In 1897 the imports were 19,114,000 pounds, valued at $270,952, and in 1900 they were 32,299,000 pounds, valued at $1,390,141. The production of the United States for the same years was 3.303,000 pounds ($56,091), and 6,193,000 pounds ($172,762), respectively.
BIBLIOGRAPHY. Newberry, "The Origin of Bibliography. Newberry, "The Origin of Graphite," in School of Mines Quarterly, vol. viii. (New York, 1887) ; Dawson, "On the Graph ite of the Laurentian, in Canada," in Quarterly Journal of the Geological Society of London, vol. xxvi. (London, 1870) ; Postlethwaite, "On the Formation of Graphite in Contact Meta morphism," in American Journal of Science, vol. xii. (New Haven, 1891) ; Downs, "Occurrence, Treatment, and Application of Graphite," series of articles in the Iron Age (New York, 1900) ; Weinschenk, Zur Kenntniss der Graphitlager statten (Munich, 1897). For statistics of pro duction and notes in regard to the trade, consult The Mineral Industry, vols. i. to x. (New York,