Diamonds and pencil lead are made of the exact same ingredient: carbon.

Carbon atoms can arrange themselves in different patterns called allotropes. In a diamond, every carbon atom bonds tightly to four other atoms. This creates a pyramid-like shape called a tetrahedron. This 3D structure is so strong that diamonds are the hardest natural material on Earth.Graphite is the form of carbon found in pencils. In graphite, atoms bond to only three other atoms to form flat sheets. These sheets look like a honeycomb pattern. The layers are held together by very weak forces. This allows the layers to slide off the pencil and onto the paper when you write.Natural diamonds form deep inside the Earth. They are created about 150 to 200 kilometers below the surface. This process requires temperatures over 1,000 degrees Celsius. It also needs pressure about 50,000 times higher than the air around us.In 1772, a chemist named Antoine Lavoisier used a giant magnifying glass to burn a diamond. He proved it was carbon because it turned into carbon dioxide gas. In 1797, Smithson Tennant showed that burning the same amount of diamond and graphite produced the same amount of gas. This proved they were chemically identical.