Which mechanism explains why index minerals indicate specific pressure-temperature metamorphic facies?

💡 Explanation

Mineral assemblages are stable only within defined pressure-temperature ranges, because the Gibbs free energy is minimized under those specific conditions. Therefore, facies are mapped using index minerals, rather than assuming uniform mineralogy regardless of metamorphic grade.

• What causes higher rates of groundwater infiltration through sandy soil, compared to clay-rich soil?
• If silver nanoparticles are ingested by zooplankton at the base of a freshwater food web, which consequence affecting higher trophic levels is most likely?
• A persistent northerly wind blows along the west coast of a continent. Which consequence follows?
• If the Earth's rotation were to slow significantly, which consequence follows regarding the paths of prevailing wind streams?
• What happens to cation exchange capacity (CEC) in soil when silicate minerals weather and release silicon?
• If a newly formed freshwater wetland experiences sustained flooding with stagnant water, which consequence is most likely?