Pure carbon takes radically different forms depending on how its atoms are arranged:

• Diamond — each carbon bonds to four others in a rigid 3D lattice. Result: the hardest natural material, transparent, and electrically insulating
• Graphite — carbons form flat hexagonal sheets that slide over each other. Result: soft, black, conductive, and perfect for pencils
• Graphene — a single sheet of graphite, one atom thick. Stronger than steel, transparent, and conducts electricity better than copper
• Fullerenes — carbon atoms arranged into hollow cages or tubes. The most famous is buckminsterfullerene (C60), a soccer-ball-shaped cage of 60 atoms, with promise in medicine and electronics