Carbon is the sixth most abundant element in the earth. The property of an element to take more than one physical form is called allotropy and the different forms are called allotropes. As allotropes take different chemical structures, they exhibit different properties as well. Carbon exists in three basic forms in nature – diamond, graphite and fullerite.
What are minerals?
Diamond is the hardest substance known. Each atom in diamond is linked to four other carbon atoms through covalent bonds. As the valence electrons are not free to move, it is a poor electrical conductor. The network of covalent bonds is very strong to break and hence the melting point of diamond is very high. It is a good thermal conductor and is used for cutting, grinding tools and making jewelry.
The softest form of carbon is the graphite. Each carbon atom is linked to only three other carbon atoms to form sheets of carbon atoms. Since the fourth carbon atom is free to move, it is a good conductor of electricity. The melting point of graphite is more than that of melting point of diamond because of a stronger covalent double bond existing between two carbon atoms in graphite. Graphite mixed with clay is used to make pencils and are used in making electrodes found in the batteries.
Fullerite is an allotrope that was not known until 1985. It is a mineral made up of molecules each comprising exactly 60 carbon atoms arranged in a form of sphere. The properties and uses are still under study.