Final answer:
Diamonds are commonly found in kimberlite, distinguished by their strong carbon bonds forming a hard structure, in contrast to the weaker, layered structure of graphite.
Step-by-step explanation:
Diamonds, known for their hardness and brilliance, are typically found in a type of rock called kimberlite. While both diamond and graphite are composed of carbon, their properties differ drastically due to the arrangement of carbon atoms. Diamond is composed of sp³ hybridized carbon atoms, each bonded to four other carbon atoms in a tetrahedral array, forming a giant molecular structure.
This strong bond in all directions contributes to the extreme hardness of diamonds, allowing them to have high melting points and make them excellent substances for cutting tools and jewelry. Conversely, graphite has a layered structure with weak attractions between the carbon layers, which is why it rubs off onto paper in pencil lead.