Which mineral is commonly associated with granulite facies metamorphism?

• A. Quartz
• B. Sillimanite
• C. Almandine
• D. Biotite

Answer: (B)

In metamorphic rocks, the minerals that crystallize reveal the temperature and pressure conditions during formation. Granulite facies rocks form at very high temperatures, and under these conditions sillimanite becomes stable among the aluminum silicates. Sillimanite indicates the hot, dehydration-driven conditions characteristic of granulite facies, making it a reliable indicator of this high-grade metamorphism. Quartz is common across many metamorphic rocks and doesn’t pinpoint granulite-grade conditions. Almandine garnet can occur in various high-grade rocks, so it’s not as diagnostic for granulite specifically. Biotite tends to be stable at lower temperatures and is less typical in granulite rocks, where it fades away with very high temperatures. Hence, sillimanite is the mineral most commonly associated with granulite facies metamorphism.