1. n. [Geology]
A change of preexisting rocks or minerals caused by the activity of hot solutions, such as fluids accompanying or heated by magma. Quartz, serpentine and chlorite are minerals commonly associated with hydrothermal alteration. Ore deposits, such as lead (as the mineral galena), zinc (sphalerite), and copper (malachite), can occur in areas of hydrothermal alteration.
See: chlorite, hydrothermal, igneous, magma, mineral, quartz