Will diamonds burn in a cremation retort?

Customarily, according to Wikipedia, below: " Jewellery, such as necklaces, wrist-watches and rings, are ordinarily removed before cremation, and returned to the family."

Otherwise, some processes strain human ashes for metal fragments, which are increasingly recycled. A diamond stone would certainly survive cremation: it has the highest melting temperature of any mineral which is not approached during a commercial cremation process.