Formation
(1) Magmatic, formed by slow cooling and crystallization from acidic to intermediate melts (especially in pegmatites) at temperatures below the monoclinic-triclinal stability point (approx. 450–500 °C)
(2) Metamorphic, formed by recrystallization or metasomatic processes in the amphibolite to granulite facies, as well as by the prolonged thermal ordering (Al/Si ordering) of orthoclase during cooling.
