fluidrock

Fluidrock is a term used in geology to describe rocks whose history includes substantial interaction with circulating fluids within the Earth’s crust. It is not a distinct rock class, but a descriptive label for rocks that have undergone metasomatic alteration as hydrothermal or other fluids moved through their mineral structure, changing texture and chemical composition.

Formation and processes occur when fluids originate from metamorphic dehydration, magmatic vapors, or meteoric water and migrate along fractures and faults. Through fluid–rock interaction, existing minerals may dissolve while new minerals precipitate, forming vein networks and alteration halos. Temperature, pressure, pH, and fluid composition govern the resulting mineral assemblages, which can include quartz, calcite, chlorite, epidote, sericite, and sulfide phases. The outcome is a rock carrying both solid and fluid histories, sometimes also described as metasomatic or hydrothermally altered rock.

Characteristics of fluidrock often include changes in color, hardness, and porosity, as well as distinctive mineral assemblages in altered zones. Fluid inclusions trapped within minerals can preserve information about the temperature and composition of the fluids during mineral growth, aiding interpretation of the rock’s history.

Occurrences and significance are broad in geology. Fluidrock signatures are common in hydrothermal ore deposits, geothermal reservoirs, and ancient metamorphic belts. Studying fluidrock alteration helps locate ore zones, understand crustal fluid circulation, and reconstruct past thermal and chemical conditions in the crust.