 In metamorphic petrology an authigenic mineral is one formed "in situ" during metamorphism, again by precipitation from fluids or recrystallization.For any mineral to be precipitated, the water must be oversaturated with respect to that mineral.For calcite, this means that the area of deposition must be above the carbonate compensation depth, or that the pore waters are sufficiently saturated due to dissolution of other grains that precipitation can begin.