The two most common and well-known allotropes of carbon are graphite and diamond. They are both made of carbon atoms arranged in different ways but they differ significantly in their properties. While diamond is the toughest natural mineral with a hardness of 10, graphite is soft and slippery.
This difference is due to the nature of the bonds between the carbon atoms. Diamonds have strong covalent bonds between carbon atoms but in graphite, these are weak and the layers can easily slide over one another. This also allows the fourth electron (the extra one from each carbon atom in a covalent bond) to wander freely over the surface of the layer, which makes graphite an excellent electrical conductor.
In addition, the weak intermolecular forces between layers make graphite more pliable than diamond and it can be drawn into thin sheets that are easy to handle. This is why it is used as the main ingredient in pencils. Moreover, it is an important component in the production of carbon electrodes, brushes, and plates for lithium-ion batteries. Graphite is also an effective lubricant and is useful in preventing metal parts from wearing away too quickly.
While it is dangerous to inhale carbon dust for extended periods of time, its use is important since it can protect metal surfaces from corrosion. It also serves as a key component in repellant solutions such as the famous WD-40. Lastly, powdered graphite is mixed with paints to produce authentic wall protection.