Which statement about diamond and graphite is true?

• A. They are both carbon, but have identical crystal structures and form in the same environments
• B. Diamonds and graphite have completely unrelated chemical compositions
• C. Diamond and graphite are both carbon, but have different crystal structures and form in very different environments
• D. Graphite is metallic and hard; diamond is a gas at room temperature

Answer: (C)

Carbon can exist in several different forms, or allotropes, because the bonds between its atoms can arrange in distinct ways. Diamond and graphite are both carbon, but they differ in how the atoms are bonded and how those bonds extend through the structure.

In diamond, each carbon atom forms strong covalent bonds in a three-dimensional network (sp3 bonding), creating a rigid tetrahedral lattice. This extensive 3D bonding gives diamond remarkable hardness and a high refractive index. Diamond forms under very high pressure and temperature deep in the Earth’s mantle and is brought toward the surface by special volcanic activity.

Graphite, on the other hand, is built from layers of carbon atoms bonded in a two-dimensional hexagonal lattice (sp2 bonding). The layers glide over each other because the forces between them are weak, so graphite feels slippery and conducts electricity along the layers. It forms under different, often lower-pressure conditions and from carbon-rich metamorphic or sedimentary environments.

So the true statement recognizes that both materials are carbon, but their crystal structures and formation environments are distinct.