Diamonds and graphite are both made of carbon atoms, but they have very different structures. Diamonds have a cubic crystal structure, while graphite has a hexagonal crystal structure. This difference in structure causes diamonds to be very hard and strong, while graphite is soft and brittle.

Diamonds are formed when carbon atoms are subjected to extremely high pressure and temperature. This can occur naturally when carbon-rich rocks are buried deep within the Earth's mantle. The high pressure and temperature cause the carbon atoms to rearrange themselves into the cubic crystal structure of diamond.

Graphite can be transformed into diamond by a process called chemical vapor deposition (CVD). In this process, a mixture of methane and hydrogen gases is passed over a heated substrate. The carbon atoms in the methane gas react with the hydrogen atoms to form carbon-hydrogen bonds. These bonds then break down, releasing carbon atoms that can attach themselves to the substrate. Over time, a thin layer of diamond can be deposited on the substrate.

CVD diamonds are typically used in industrial applications, such as cutting tools and abrasives. They are also used in some high-end jewelry applications.