Diamond is a

Diamond is an allotrope of carbon characterized by its extreme physical properties. It is recognized as the hardest naturally occurring substance known, scoring a 10 on the Mohs scale of mineral hardness [1]. This hardness arises from its rigid three-dimensional tetrahedral structure where each carbon atom is covalently bonded to four others [4]. Regarding electrical properties, diamond is a non-conductor (electrical insulator) because all its valence electrons are tightly held in these covalent bonds, leaving no free electrons to carry an electric current [3]. While it is an exceptional thermal conductor, its high electrical resistivity (ranging from 10^12 to 10^13 ohm-m) classifies it as an insulator [2]. In contrast, graphite, another carbon allotrope, is soft and a good conductor due to its layered structure and free electrons [4].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Allotropes of carbon > p. 61
2. [4] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > Table 3.1 > p. 40
3. [2] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > Activity 11.3 > p. 179
4. [3] Science-Class VII . NCERT(Revised ed 2025) > Chapter 4: The World of Metals and Non-metals > 4.1.5 Conduction of electricity > p. 48