Granite classification distinguishes hypersolvus granites (crystallizing at high temperature and/or low water pressure, where a single homogeneous alkali feldspar solid solution remains stable without unmixing) from subsolvus granites (crystallizing at comparatively lower temperature and/or higher water pressure, where the alkali feldspar composition falls within the solvus miscibility gap, producing two distinct feldspars — K-feldspar and Na-plagioclase, or perthitic exsolution of one into the other upon slow cooling).
Granite A, showing two distinct feldspars (K-rich and Na-rich) with exsolution textures, is a subsolvus granite: its alkali feldspar composition crystallized within the solvus miscibility...
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