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Cryptoperthitic alkali feldspars in the Cerro Colorado monzonites from the Atacama Desert, northern Chile, exhibit bluish iridescence. Three types of cryptoperthites are developed over a grain; fine and coarse cryptoperthites of Or-Ab-An ternary compositions around Or(60-65)Ab(35-30)An(5), and Or-rich, An-poor cryptoperthite around Or(70)Ab(26)An(4). The former ternary compositions point to crystallization at approximately 900 degrees C. Hydrothermally turbid patch microperthites are not developed in the alkali feldspar, whereas turbid Or-rich veins with micropores display limited replacement of the cryptoperthites along the lamellae. The Or-rich veins are much richer in water than the cryptoperthitic regions. Blue cathodoluminescence of variable tint is observed over individual grains, except in the Or-rich veins. The Cerro Colorado alkali feldspars record an incipient state of alkali feldspars, which predates the low-temperature formation of patch microperthite in subsolvus granites. These feldspars are the first natural alkali feldspars with K-feldspathization without microperthite formation.