Those of other liquids may be determined by comparing their gravities with the gravity of water. See pressure gradient . That level, which for a given point in an aquifer, passes through the top of a column of water that can be supported by the hydrostatic pressure of the water at that point. The weight of formation fluid filling the pores of the rock and in communication with the water table at the well site, or sea surface. Usually the fluid is considered to be formation water .
Hydrothermal solutions are of diverse sources, including magmatic , meteoric , and connate waters .
The phase changes resulting from the interaction of hydrothermal fluids with pre-existing solid phases. Included are the chemical and mineralogical changes in rocks brought about by the addition or removal of materials through the medium of hydrothermal fluids.