Graphite is an opaque, non-metallic carbon polymorph that is blackish silver in colour and metallic to dull in sheen. Since it resembles the metal lead, it also known colloquially as black lead or plumbago.
Formation of graphite
Graphite is most often found as flakes or crystalline layers in metamorphic rocks such as marble, schists and gneisses. Graphite may also be found in organic-rich shales and coal beds. In these cases, the graphite itself probably resulted from metamorphosis of dead plant and animal matter. Graphite is also found in veins and sometimes in basalt. Graphite also occurs in meteorites.
Molecular structure of graphite
Graphite consists of a ring of six carbon atoms closely bonded together hexagonally in widely spaced layers. The bonds within the layers are strong but the bonds between the layers are less in number and therefore weaker. Graphite is therefore soft and flakes easily. Graphite is the stable form of carbon - diamonds at or near the Earth"s surface are gradually changing to graphite. Fortunately this process is extremely slow.
Differences between graphite and its carbon polymorph, diamonds
Diamond is another carbon polymorph; although composed of the element carbon, like graphite, diamond does not have much else in common. Each has a lot of contrasting properties. For instance, diamond is the hardest mineral, but graphite is one of the softest. Diamond is usually transparent, but graphite is opaque. Also, diamond is often used as an abrasive, whereas graphite makes a good lubricant. Graphite is an excellent conductor of electricity, while diamond makes a good electrical insulator.
Uses of graphite
Named in 1789 by the German chemist and mineralogist A.G. Werner, the name for graphite is derived from the Greek word, graphein, which means: to write. The name therefore denotes the primary use of graphite as an ingredient used to make the lead for writing pencils. Other uses of graphite include:
- Additive in ceramics
- Aerospace: Rocket Nozzles, Stealth F-117A and B2 bomber aircraft
- Baseball Bats: (graphite and kevlar composite)
- Canisters & Aluminum Extrusion Boards
- Chemical: Vessels and Reactors, Bushings, Bearings, Packing Rings, Seals, and Rollers
- Electrical, Electrochemical, Electronic, Electrodes, Semiconductor: Brushes, Anodes, Cathodes, Current Collectors, Sliding Contacts, EDM Electrodes
- Fluxing (Degassing) Tubes, Molds, Dies, Furnace Parts, Foundry Accessories
- Graphite electrodes
- Guides, Valves, Rotors & Vanes
- Metallurgical Crucibles
- Nuclear: High Purity Structural Components, Reflectors, Moderators
- Resistors, Brazing Tips, Heaters, Seed Holders
- Hardener in steel making
History of the pencil
Graphite was first discovered in Cumbria in North England at the beginning of the sixteenth century. Although it resembled coal, it would not burn. It did, however, prove to be an excellent marker of sheepskins.
The government of England took charge of the mining operations of graphite when it was discovered that it also served as an excellent mould for cannonball production. As such, the value of graphite increased dramatically in a short period of time. During the reign of Queen Elizabeth I, graphite was transported to the capital under cover of the local guard.
Dubbed "Wad" by the locals, graphite soon became a precious commodity. In 1752, the government made the stealing and trade of stolen graphite a criminal offense, punishable by hard labour or transportation.
The first documented use of graphite as a pencil occurred in 1565. The use of graphite as an art material became popular, sold by Flemish merchants throughout Europe. At first, pencils consisted of rough pieces of graphite wrapped in sheepskin. The Italians first began using pencils that consisted of pieces of graphite embedded in wood.
In the early days of pencil making, a small cottage industry started in Keswick, England making artists' pencils. These were all made by hand and the method was briefly as follows:
A piece of Cumberland Graphite was cut into slabs. A square groove was then carved into a piece of wood. The slab of graphite was inserted in the groove; the graphite was then broken off, so that it was level with the top of the groove; a thin slat of wood covered the graphite, leaving the graphite encased.
This wood was shaped by hand-plane and the shape of the knife in the plane determined the shape of the pencil, round, oval, etc., and all this work was carried out by hand. Later, small primitive types of lathes were introduced which were foot-operated with a treadle similar to a treadle sewing machine and all the shaping was done in this manner. All the pencils were hand-made; many families in Keswick made these pencils in their cottages, the origin of the pencil industry.
In the mid-eighteenth century, the relationship between Britain and France deteriorated. As a result, supplies of graphite from England to France dried up. In 1795, the French artist Conte discovered that graphite could be mixed with clay to produce pencils with varying degrees of hardness. In the mid-1830s, the pencil making industry in Keswick had started to set up factories; it turned more and more to the use of powdered graphite mixed with powdered clay to make pencils.
Plumbago Mine, Borrowdale, England:
This mine was famous for producing graphite that did not come from bedded shales or embedded in rock but was associated with an igneous intrusion connected to a hydrothermal vein that contained wads of graphite along it. The mineral was found along a 400 m stretch of the vein in lumps and nodules. A market for it opened up around the end of the sixteenth century. German miners from Keswick in the early sixteenth century had made more progress mining the graphite from the site.
Lots of graphite could be mined in a short period of time with little expense so in order to maintain the sale value of the graphite, the owners of the mine agreed not to reopen it for a certain period of time. As a result, stealing of graphite, or "wad" as they called it at the time, became quite common. For that reason, a security lodge was built outside the upper part of the mine, with an armed guard to keep watch over the mine day and night. In the 1760s, the mine briefly reopened but only eight workmen were chosen to mine it. Several times each day the miner"s pockets were checked by six different overseers, to make sure that they were not stealing any wad while mining it.
In 1800, the Grand Pipe was finally dewatered, which opened other parts of the mine, which could be used for the extraction of graphite. Workmen continued to mine the cave for graphite and three year later, their efforts were rewarded by the surprisingly late discovery of a large accumulation of wad known as Dixon"s Pipe.
First graphite mine in Canada
Canada's first graphite mine was the Miller (Keystone) mine, Grenville, Quebec.
Graphite from Ontario
Graphite is found primarily among the rocks of the Precambrian Grenville Province of Eastern Ontario.
In 1889 graphite was discovered on the shore of Whitefish Lake, Renfrew County. This later became Ontario"s richest graphite mine, the Black Donald Mine. The graphite mine location is now under the waters of Black Donald Lake. People may visit the town site by scuba diving.
Graphite was mined at the National Graphite Mine, Graphite, Monteagle Township, near Bancroft. The mine operated from 1912 to 1919.
Graphite spheres embedded in crystalline calcite were found exposed by a roadcut on Haliburton County road about 3.6 km south of Gooderham, Ontario, Canada.
Graphite from Mine in Cesky Krumlov:
The mine in Cesky Krumlov was first discovered around 500 BC in Southern Bohemia in the outskirts of the small village of Cesky Krumlov. The graphite was mined by the Celts as an additive to ceramics. The first modern mining of graphite took place around the middle of the 18th century. The mine became famous for its rich deposits of graphite with layers that were about 1 metre - 20 metres in thickness and extended for, at times, over one kilometre.
During the mid-eighteenth century, graphite first began to be mined by modern methods at Cesky Krumlov. Other graphite mines were found nearby. The presence of lots of highly metamorphosed rocks such as gneisses were found along the two rivers known as the Danube and the Vitava (which was called the Moldau in German). The entire geologic structure was thus dubbed the moldanubic crystallinicum as it incorporates the names of both rivers and refers to the crystalline structure of the gneisses found there that contain graphite.