GRAPHITE (Fa., Graphite ; Gan., Graphit).
Graphite is also called " plumbago " and " blacklead," misnomers associated with the erroneous Idea that lead enters into its composition. This valuable mineral is now recognized as a native form of carbon ; its chemical properties, however, have yet to be fully discovered, and geologists are still at variance concerning its probable origin ; on these points, therefore, only so much will be said as has a practical bearing upon the applications of the substance. Two distinct varieties are noticed : the one, fine-grained, or amorphous ; the other, foliated, or compounded of numerous little scales; sometimes also it appears as an impregnation of other rocks, rather than as a distinct rook in itself. Geologically, it is confined to the oldest formations, and is usually, if not universally, associated with metamorphio action.
Its geographical distribution includes all five quarters of the globe. Among European localities, the first place must be assigned to the historically renowned mines of Borrowdale and Keswick, in Cumberland. These were revealed by an accidental occurrence, and were worked as early as 1644. The value and scarcity of the mineral severely provoked the thieving propensities of the neigh bouring population, so much so that special legislation was needed in 1752 to protect the owners. In 1788, the output was 417 casks (each containing 70 lb.) of the best quality, whose value was estimated at 45,0001. In 1804, when the price was 35s. a lb., the nett profits reached 118,8751. The entrance to the mine was enclosed by a stout building, and the workmen were searched on leaving. The graphite found here is of the fine-grained or amorphous variety, containing from 95 to nearly 100 per cent. of carbon, the impurities being usually small quantities of silicates. The mineral, which is locally known as " wadd," occurs in nests, " sops," " bunches," or " cells," in a partially decomposed trap-rock, running through clay-slate ; it is worked by means of "stages," "veins," and "pipes." These mines were for many years the sole known source of graphite, and their productive capabilities were so great that it was only necessary to work them for a few months in order to supply the markets for several years. During the intervals of idleness, means were adopted for flooding the workings with water, as the surest preventive of stealing.
Late in 1875, the mines were reopened, after having been closed for an unusually long time, on account of private and legal difficulties. The protracted inactivity had given rise to rumours that the deposits were exhausted, but nests have recently been discovered of as large dimensions and as good quality as hitherto. For the purpose of pencil-making, it remains unequalled by that from any other source. The minor occurrences of the mineral in the United Kingdom are :—in gneiss, at Glenstrathfarrar, in Inverness ; in coal-beds which have been formed in contact with trap, at Craigman, in Ayrshire ; and in small lumps, in the elvan courses of Cornwall.
Germany possesses several graphite deposits. A variety about equal in purity to that of Cumberland, but somewhat more amorphous and friable, occurs in considerable quantities at Griesbach, near Passau, in Bavaria. It is not refractory, and is therefore valueless for crucible making, and is of little use as a lubricator ; but for pencils, it is largely employed, and is imported into this country for making domestic blacklead (stove-polish). In the Adelheids-Gluck coal mine, at Rybnik, Prussian Silesia, an important layer of graphite earth has been found, in thickness exceeding 40 ft. Trials are said to have proved it well fitted for luting, muffles, hearths, &c. A specimen of graphite from Styria exhibited coarsely foliated structure, strong metallic lustre, and sp. gr. 2.1443. Its composition was :—Carbon, 82.4 ; silica (belonging to the ash), ; alumina, ; peroxide iron, ; protosesquioxide manganese, 0.62 ; lime, 0.02 ; alkalies, traces. The production of graphite in the Austro-Hungarian Empire was 203,166 metrical centners (of 110i lb.) in 1875, and 127,171 in 1876. Spain has lately sent some graphite of fair quality to this country. An analysis of Portuguese graphite gave :—Water (including hygroscopic), 10.21 ; carbon, ash, 50.81. A sample from Upernavik, Greenland, hard and of pale colour, useless for pencils, showed :—Carbon, 96.6 ; ash, 3.1 per cent. An occurrence of graphite with quartz is reported from Arendal, Norway. The mineral has also been found in Finland.