Propylitic alteration
Encyclopedia
Propylitic alteration is the chemical alteration of a rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

, caused by iron and magnesium hydrothermal fluids, altering e.g. biotite or amphibole groundmass material.
It typically results in epidote–chlorite–albite alteration.

The alteration occurs in hot fluids that have a high sodium ion composition. This is typically due to fluids that have lost potassium ions in potassic alteration and gained sodium ions.
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