Aqueous fluids are the agents of geologic change.
They initiate and control many geologic processes because they are ubiquitous, mobile, and chemically reactive. Chemical interaction between fluids and rocks within the earth has a direct bearing on topics as diverse as drinking water quality, waste disposal, geothermal energy, economic ore formation, metamorphism, volcanism, and ultimately the chemical evolution of the atmosphere, hydrosphere, and lithosphere. We will begin by briefly reviewing the background material of geochemistry, then proceed from low-temperature to high temperature fluid chemistry. Low-temperature geochemistry will be treated first because it is a much more mature field of investigation and therefore is covered in many textbooks. Because it is a mature field, there exists a large database of thermodynamic quantities that allows us to quantitatively estimate equilibrium fluid compositions, which we will do in several problem sets.