Here's why:

* Lack of metallic properties: Carbon doesn't have the typical characteristics of metals, such as:

* Luster (shininess)

* Malleability (ability to be hammered into thin sheets)

* Ductility (ability to be drawn into wires)

* Good conductivity of heat and electricity

* Forms covalent bonds: Carbon primarily forms covalent bonds with other elements, sharing electrons rather than losing or gaining them like metals do.

* Exists in various forms: Carbon can exist in different forms, including graphite (soft and slippery), diamond (hardest natural material), and fullerenes (cage-like structures). These diverse forms further indicate its nonmetallic nature.

While carbon can sometimes behave in ways that resemble metals in certain situations, it's fundamentally categorized as a nonmetal.