Under conditions of high temperature and decreased pressure during emplacement, what happens to diamonds?

Under conditions of high temperature and decreased pressure during emplacement, what happens to diamonds?

• A. Remain diamonds
• B. Convert to graphite
• C. Melt into carbon vapor
• D. Oxidize to carbon dioxide

Answer: (B)

Diamonds are the high-pressure form of carbon, while graphite is the stable form at low pressure. When a rock containing diamonds experiences high temperature and a drop in pressure during emplacement, the diamond structure becomes thermodynamically unstable and can rearrange into graphite. This rearrangement, called graphitization, is favored because graphite is the stable phase of carbon under those conditions, and heat helps the carbon atoms migrate into the layered graphite arrangement. The other outcomes—remaining as diamonds, melting into carbon vapor, or oxidizing to CO2—are not the typical pathway under these conditions; graphitization is the dominant transformation when pressure drops and heat is present.

Diamonds are the high-pressure form of carbon, while graphite is the stable form at low pressure. When a rock containing diamonds experiences high temperature and a drop in pressure during emplacement, the diamond structure becomes thermodynamically unstable and can rearrange into graphite. This rearrangement, called graphitization, is favored because graphite is the stable phase of carbon under those conditions, and heat helps the carbon atoms migrate into the layered graphite arrangement. The other outcomes—remaining as diamonds, melting into carbon vapor, or oxidizing to CO2—are not the typical pathway under these conditions; graphitization is the dominant transformation when pressure drops and heat is present.