Andalusite, kyanite, and sillimanite are among the best known index minerals that provide information about the temperature and pressure of metamorphism.

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Andalusite, kyanite, and sillimanite are known as the "sillimanite group" and are commonly used as index minerals in metamorphic petrology to determine the temperature and pressure conditions of metamorphism.

Andalusite, Kyanite, and Sillimanite Are Among the Best Known Index