Remanence; the magnetization remaining in the absence of an induced magnetic field. (a) Normal remanent magnetization (NRM) is the residual magnetization possessed by rocks and other materials in situ; unless otherwise qualified, this is the meaning implied. (b) Thermoremanent magnetization (TRM) remains after a sample has been cooled to a temperature below the Curie point in a magnetic field. (c) Chemical remanent magnetization (CRM) is acquired when a magnetic substance is chemically formed or crystallized in a magnetic field at temperature below the Curie point. (d) Depositional (or detrital) remanent magnetization (DRM) is acquired in sediments when magnetic mineral particles are preferentially aligned by the ambient magnetic field during deposition (usually by settling through water). (e) Isothermal remanent magnetization (IRM) is remanent magnetization in the ordinary sense, i.e., the magnetization after application and subsequent removal of a magnetic field; it is not involved in paleomagnetism, except for the effect of lightning currents in exposed surface rocks. (f) Pressure (or piezo) remanent magnetization (PRM) is remanence acquired as a result of the application of stress; the effects generally become more pronounced as the strain proceeds from elastic to plastic deformation. See also viscous magnetization.