Carbon can be found naturally in two crystalline forms: graphite and diamond. Both are chemically similar but quite different in physical properties and crystal structure. Graphite is a crystalline and soft form of carbon. It is a distinct substance that possesses both metal and non-metal qualities. 

Graphite is named from the Greek word ‘graphein’, which means ‘to write’. It can be found in igneous and metamorphic rocks. It is usually found in a greyish-black colour. It is opaque and has a shiny black sheen. It has low specific gravity and is a soft mineral. When carbon is exposed to heat and pressure in the Earth’s crust, graphite is formed.

Types of graphite

There are two types of graphite: natural and synthetic. 

Natural graphite

It is a mineral naturally found in the Earth’s crust. It is made up of graphite and carbon. This form of graphite is mined. If it is combined with other minerals, it is extracted. Mineral processes, such as flotation and filtering, are required for its extraction.

Natural graphite is a good heat and electricity conductor and can withstand a wide range of temperatures.

On the basis of crystallinity, this mineral can be divided into three categories:

• Highly crystalline 
• Amorphous 
• Flakey

Synthetic graphite

Synthetic graphite can be produced from coke and pitch. It is not as crystalline as natural graphite but is purer than the latter. 

There are two types of synthetic graphite:

• Electrographite: It is pure carbon that is produced from coal tar pitch and petroleum coke.
• There is another form of synthetic graphite produced by heating calcined petroleum pitch.

Structure of graphite

Graphite has a covalent structure, which implies that each carbon atom in the graphite molecule is connected by covalent bonds to three other carbon atoms. The carbon atoms are organised hexagonally to form a sheet-like structure. This structure is held in place by weak forces.

Multiple sheets of carbon atoms are parallelly arranged. The atoms in graphite show sp2 hybridization. Graphene refers to the individual layers of graphite. The carbon atoms in each layer are organised in a honeycomb lattice, with 0.142 nm bond length and 0.335 nm plane separation. Atoms in each layer are separated by 2.5 times the space between them.

In the structure of graphite, each carbon atom uses three electrons to create simple connections with the electrons of its three nearest neighbours. At the bonding level, the fourth electron remains. This ‘spare’ electron in each carbon becomes delocalized across the entire sheet of atoms in one layer.

Properties of graphite

Physical properties

• Electrons in graphite’s structure are delocalized and free to travel throughout the sheet. It makes graphite an excellent conductor of electricity.
• Graphite is insoluble in organic solvents and water because the attraction between carbon atoms and solvent molecules is weak and not enough to break covalent bonds.
• It has a high melting point, the same as that of the diamond.
• It has a sheet-like structure, due to which it is soft and slippery.
• Graphite also has the ability to absorb high-speed neutrons.

Chemical properties

• Reaction with air: The carbon in graphite reacts with oxygen to form carbon monoxide and carbon dioxide, depending on the availability of oxygen.
• Reaction with water: Naturally, graphite does not react with water. But under certain circumstances, it reacts with water to produce carbon monoxide and hydrogen.

Application of graphite 

• Graphite is used as a refractory material, such as Mag-carbon refractory bricks. It is also used in making crucibles and moulds.
• It is used in making furnaces where steel and iron are processed.
• Graphite anodes are used in the electrolysis process.
• It is used to manufacture paints, pencils, and other things.

Conclusion

Graphite is a crystalline form of carbon, apart from diamond. It is a soft and naturally occurring mineral form of carbon. The structure of graphite is interconnected hexagonal sheets. There are two kinds of graphite, natural and synthetic. The colour of graphite is greyish black. It is found naturally in the earth’s crust from where it is extracted. Graphite is used in metallurgy, coating, and paint manufacture, among other things.