If you heat a diamond to about 763° Celsius (1405° Fahrenheit), it will turn to vapor.
 
At normal temperatures and normal pressure, a diamond is hard as a rock. In fact, diamonds are some of the hardest rocks on Earth. At normal atmospheric pressure, diamonds will not evaporate at all.
 
If diamonds are too tough to evaporate, how do they turn to vapor?
 
They oxidize. Oxidation describes a chemical reaction in which oxygen interacts with other substances. Oxygen is a major part of our atmosphere, and substances oxidize all around us, all the time. Rust, for instance, is an example of the oxidation of iron. Rust is also known as iron oxide.
 
Diamonds are a form of pure carbon. As carbon oxidizes, the chemical reaction forms the everyday gases carbon dioxide and carbon monoxide. These are the vapors that a diamond becomes at such high temperatures.
  • In non-oxidizing conditions under normal pressure, diamonds can be heated to about 1,900° Celsius (3,452° Fahrenheit) before changing their crystal structure.
  • In non-oxidizing conditions at extremely high pressure (197,385 atmospheres), diamonds can withstand temperatures of up to 3,500° Celsius (6,332° Fahrenheit) before changing their crystal structure.
  • In the absence of oxygen, diamonds can be heated to much higher temperatures. Above the temperatures listed below, diamond crystals transform into graphite. The ultimate melting point of diamond is about 4,027° Celsius (7,280° Fahrenheit). 
Noun

layers of gases surrounding a planet or other celestial body.

Noun

force per unit area exerted by the mass of the atmosphere as gravity pulls it to Earth.

chemical reaction
Noun

process that involves a change in atoms, ions, or molecules of the substances (reagents) involved.

diamond
Noun

type of crystal that is pure carbon and the hardest known natural substance.

evaporate
Verb

to change from a liquid to a gas or vapor.

gas
Noun

state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.

oxidize
Verb

to combine with oxygen to form a different compound (oxide).

pressure
Noun

force pressed on an object by another object or condition, such as gravity.

rust
Noun

red or orange coating that forms on the surface of iron when it is exposed to oxygen and moisture. Also called iron oxide or ferric oxide.

Noun

degree of hotness or coldness measured by a thermometer with a numerical scale.

vapor
Noun

visible liquid suspended in the air, such as fog.

vaporize
Verb

to turn into gas, or vapor.