Here's why:
* Resistant to Chemical Change: Quartz is extremely resistant to chemical weathering and alteration. It can withstand the high temperatures and pressures associated with metamorphism without significantly changing its chemical composition.
* Wide Range of Stability: Quartz is stable over a wide range of metamorphic conditions, from low-grade (e.g., slate) to high-grade (e.g., gneiss) metamorphic rocks.
* Abundant in Earth's Crust: Quartz is a very common mineral, making it a frequent component of metamorphic rocks.
While other minerals like feldspar, mica, and garnet may be present in some metamorphic rocks, their presence and abundance vary depending on the metamorphic grade. Quartz, however, is a constant companion, providing a strong indicator of metamorphic processes.
