How does calcination occur?

Calcination is a process that specifically refers to the thermal decomposition of materials, where they lose water or other volatile materials when exposed to heat. In the context of the question, gypsum, which is a mineral composed mainly of calcium sulfate dihydrate, undergoes calcination when it is heated. During this heating process, it loses water and transforms into calcium sulfate hemihydrate, commonly known as plaster of Paris. This transformation is significant in construction and fire safety because it illustrates how gypsum wall surfaces can respond to heat exposure, ultimately affecting the fire-resistance rating of a structure.

The other choices reference different phenomena that do not accurately describe calcination. Spontaneous ignition, complete combustion of wood, and crumbling plaster due to fire exposure involve other chemical and physical processes, which are distinct from the specific loss of water that characterizes calcination.