Which allotropy of carbon is in rigid three-dimensional struc- tures ?

Carbon exists in several allotropic forms with distinct structural arrangements. Diamond is characterized by a rigid three-dimensional network where each carbon atom is sp3 hybridized and covalently bonded to four other carbon atoms in a tetrahedral geometry [1]. This extensive three-dimensional lattice makes diamond the hardest known natural substance [2]. In contrast, graphite consists of two-dimensional planar sheets of hexagonal rings held together by weak van der Waals forces, allowing the layers to slide over one another [1]. Fullerenes, such as C60, are discrete molecular structures shaped like a football rather than a giant rigid lattice [2]. Carbon black is generally considered an amorphous or disordered form of carbon [3]. Therefore, diamond is the allotrope that specifically forms a rigid three-dimensional structure [2].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Allotropes of carbon > p. 61
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > Table 3.1 > p. 40
3. [3] https://www.sciencedirect.com/topics/engineering/carbon-carbon-bond