What changes can occur during metamorphism in mineral crystals?

During metamorphism, the process that rocks undergo when exposed to high pressure and temperature, significant changes can occur in the mineral crystals present within the rock. One key change is in the composition of the minerals. This can happen through various processes, including the re-crystallization of existing minerals, the introduction of new minerals as a result of chemically active fluids, or the alteration of minerals due to changes in environmental conditions.

For instance, when a limestone is subjected to metamorphism under high heat and pressure, it can transform into marble. During this transformation, the calcite in the limestone may undergo changes in its crystalline structure and composition, depending on the conditions and the presence of other elements.

While mineral crystals can indeed change in color, size, and potentially increase in temperature, these changes do not capture the core aspect of metamorphism, which fundamentally involves changes in the mineral composition. Amorphous materials are not typically the result of metamorphism, as the process usually preserves some crystalline structure. Thus, the most accurate statement regarding the changes during metamorphism in mineral crystals is that they may change in composition.