The process by which a substance changes directly from a solid state to a gas state is called sublimation. The sublimation process absorbs heat. But it should be noted that crystals can be sublimated. Amorphous crystals cannot sublimate.

Crystal means: a solid with a fixed melting point is called a crystal; Conversely, beeswax, rosin, glass, etc. There is no definite melting temperature, and they are called amorphous.