I had heard an opinion from my high school teacher, but I can't understand?? "An experimental record of a French scientist. He heats the diamond and sublimates it. After cooling, it turns back to solid barbecue carbon. In this case, although there is a physical transition, the substance seems to be a chemical change. This is just my personal opinion: the physical properties of diamonds are not suitable for describing as melting point" What??? No melting point how it transition??