Final answer:
The clay minerals transforming into mica minerals due to heat is known as neocrystallization, a key process of metamorphism that results in new minerals and altered rock textures.
Step-by-step explanation:
The transformation of clay minerals within shale into mica minerals due to the application of heat is an example of a change in mineralogy and texture within a rock as a result of metamorphism. This process is specifically known as neocrystallization, where new minerals grow at the expense of older ones in a solid-state, induced by changes in temperature and pressure. Metamorphic rocks are classified based on texture, clarity, and the types of minerals present which typically reflect the conditions of temperature and pressure they were subjected to.