Final answer:
During metamorphism, the process that changes a mineral's crystal structure without altering its chemical composition is called recrystallization. This process involves structural reformation such as aragonite to calcite, both comprising CaCO3, demonstrating a polymorphic relationship.
Step-by-step explanation:
Metamorphism and Recrystallization. During metamorphism, the process that changes the crystal structure of a mineral without changing its chemical composition is known as recrystallization. This transformation occurs under conditions of altered temperature and pressure, where minerals undergo structural changes while maintaining their original chemical formula. A common example of this is the alteration of aragonite to calcite; both share the same chemical composition, CaCO3, but have different crystal structures, making them polymorphs.
Not all metamorphic rocks exhibit the same characteristics as some minerals maintain their form during metamorphism. Rocks such as quartzite, which derive from sandstone, show minimal change and are termed non-foliated or massive. Unlike foliated rocks, such as schist or gneiss, non-foliated metamorphic rocks can resemble igneous rocks due to their lack of mineral orientation.