The melting point of diamond is 3550 degrees celcius. http://invsee.asu.edu/nmodules/Carbonmod/point.html

"Although Diamonds will withstand heat, it is possible for them to burn. In order to burn, diamonds need two things, heat and oxygen. Diamonds burn in pure oxygen at about 1320 degrees Fahrenheit. In air (which is about 20% oxygen), the temperature raises to around 1560 degrees Fahrenheit. Depending on who makes your solder, 14k solders melt between 1200 & 1500 degrees. Easy solders are at the low end and hard at the upper end. Most 18k solders are in this range, however some melt in the 1500's and 19k white weld often exceed 1600 degrees. Although most solders melt at a temperature below the burning point of diamonds the heat from the torch will often heat the diamond beyond the temperature at which it will burn. Because of this, you MUST coat the diamond with boric acid. To do this mix boric acid powder with denatured alcohol. Dip the jewelry in this mixture and light it. As the alcohol burns a coating of boric acid powder remains. When this is heated the powder melts forming a glassy coating over the diamond and jewelry. This seals out oxygen allowing you to heat the diamond to higher temperatures." source: http://www.bwsimon.com/articles/LastingForever.htm That's facetnating, huh?

Any and all elemental substances have a melting point. The melting point of a diamond, though extremely hight, does exist. Diamonds can also be burned, ask any unfortunate jeweler ; )

Everything will burn on 2012 when God replaces our blood with liquid hot magma.