During HPHT treatment, which phenomenon can occur that affects the diamond's structure and color?

• A. Graphitization can occur.
• B. The diamond always becomes colorless.
• C. The diamond dissolves completely.
• D. The surface only becomes rough without internal changes.

Answer: (A)

Graphitization can occur during HPHT treatment, where extreme heat and pressure can cause parts of the diamond’s sp3 carbon lattice to convert into graphite (sp2 carbon). This transformation changes the crystal’s structure and color, often producing darker, opaque areas and degrading transparency. HPHT can indeed alter color by reconfiguring impurities, but it doesn’t guarantee colorlessness; the color result depends on the impurities and treatment conditions. It also isn’t about the stone dissolving or only affecting the surface—internal lattice changes are a real risk with HPHT, and that’s why graphitization is the phenomenon linked to structural and color changes.