Diamond and graphite
Why are diamond and pencil lead so different?
Diamond and the graphite in a pencil are both pure carbon; the only difference is how the atoms are arranged. Same atom, different order, a completely different material.
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In three stops
Where were its atoms born?
Carbon forms when three helium nuclei fuse inside red giant stars, and stellar winds spread it into space. It is the fourth most abundant element in the universe, after hydrogen, helium and oxygen.
How did it form on Earth?
Diamond forms about 150–200 km underground, where enormous pressure and heat lock carbon atoms into a tight three-dimensional network. Deep volcanic eruptions carry them to the surface. Most diamonds are 1 to 3.5 billion years old.
What did humans make of it?
In graphite, carbon atoms form flat layers that slide over one another; rubbed on paper, the layers peel off and leave a mark. In diamond, every atom is bonded tightly to four neighbours, making it the hardest known natural material. Today diamond is used for cutting and drilling, and it can also be made in laboratories.
Did you know?
About 18% of your body's mass is carbon too. Here is the clue to what separates a person from an iron mine: what matters is less the kind of atoms than how they are arranged.