What is the purest form of carbon?

What is the purest form of carbon ?

Diamond is the purest form of carbon. Different forms of the same chemical substance are called allotropes. Graphite and diamond are two major allotropes of carbon. Diamond is a form of carbon in which each carbon atom is covalently bonded to four other carbon atoms. This forms a strong, rigid, three-dimensional structure. It is the hardest natural substance, and no other natural substance can scratch it.