Illitization processes: Series of dioctahedral clays and mechanisms of formation

The series involving dioctahedral clay minerals is, with increasing temperature, or grade: smectite → mixed-layer illite/smectite (I/S) → illite. This sequential smectite-to-illite reaction via mixed-layered minerals (“smectite illitization”) has been documented in low-temperature environments and is commonly associated with burial diagenesis, low-grade metamorphism