Here's why:

* Coal: Coal is formed from ancient plant matter that has been buried and subjected to heat and pressure over millions of years. The primary component of this plant matter is carbon.

* Graphite: Graphite is a crystalline form of carbon where the atoms are arranged in sheets. This structure gives graphite its characteristic softness and ability to conduct electricity.

* Diamonds: Diamonds are another crystalline form of carbon, but the atoms are arranged in a tightly packed, three-dimensional structure. This structure makes diamonds incredibly hard and brilliant.

So, while coal, graphite, and diamonds have very different properties, they all share the same basic building block: carbon.