A @[email protected] or @[email protected], in which the @[email protected] shows either a discontinuity (second-order) or a vertex (higher-order) at the transition temperature. Example: The transition at \(846\ \text{K}\), accompanied by a finite change in @[email protected] at constant pressure \(C_{p}\), of the low-temperature polymorph of quartz to the high-temperature polymorph.