Refers to rock constituents or minerals that have formed in place and were not transported. Such materials have formed either at the same time as the rock in which they are found or after the formation of the rock. The term is also applied to minerals that are clearly the result of new crystal growth on older crystals of the same kind, e.g., K-rich feldspar overgrowths may be referred to as authigenic overgrowths.

In a molecular dynamics simulation, the autocorrelation function is a time-dependent function calculated from the product of a quantity at a given time relative to an initial reference time. Specific autocorrelation functions are used to calculate vibrational spectra. For example, the velocity autocorrelation function is used to determine a power spectrum, and the dipole moment autocorrelation function is used to calculate the infrared spectrum.

A poorly defined material, possibly chromian illite or a mineral mixture.