Here's why:
* Abundance: Muscovite is the most abundant mica mineral, making it more likely to be found in these rocks.
* Formation: It forms during the metamorphic processes that create gneiss, granite, and schist. These processes involve heat and pressure, which transform existing minerals into new ones. Muscovite is relatively stable under these conditions.
* Appearance: Muscovite is easily recognizable with its silvery-white, pearly luster, and its ability to be peeled into thin sheets.
While biotite is another common mica, it is more often found in mafic and ultramafic rocks, which have a higher concentration of iron and magnesium.
Therefore, when considering gneiss, granite, and schist, muscovite is the most prevalent mica.
