Which statement about carbon in diamond production is correct?

• A. Diamonds form from pure graphite only
• B. Diamond and graphite have the same crystal structure
• C. Graphite is not used in diamond production
• D. Graphite is used in HPHT diamond production, and graphitization can occur for HPHT treated diamonds

Answer: (D)

In HPHT diamond production, graphite is commonly used as the carbon source, and under the right high-pressure, high-temperature conditions the carbon from graphite is arranged into the diamond crystal lattice. The same HPHT process or subsequent treatment can cause graphitization, meaning diamond can transform back toward graphite if conditions favor that conversion. So graphite is involved in producing diamond, and there is a real possibility of graphitization for HPHT-treated diamonds.

The other statements don’t fit because: diamond formation isn’t limited to pure graphite as the carbon source; carbon for diamond can come from various materials, including hydrocarbons or other carbon-bearing sources; diamond and graphite do not have the same crystal structure—diamond is a tetrahedral sp3 lattice, while graphite is a layered sp2 structure; and graphite is indeed used in HPHT diamond production, so saying it isn’t used is incorrect.