https://youtu.be/n0wvDwSnzcw?t=370 In this video it is shown how diamonds can be turned to CO2 via heat and oxygen. Though not super practical this would be cool.
Or you can create a element named Crystal (CRYT)?
Maybe create a new element, Sapphire(SPHR), that could break and melt under only the most extreme enviroments. That would mean: 1: Destructible DMND-Like Material. 2: DMND wouldn't have to change. 3: New element. If you're looking for realism, then make Broken Diamond(BDMD) that would undergo realistic processes in the right enviroments.
bruhhhh