Typically hydrothermal solutions are extremely saline and frequently contain substantial amounts of rare elements. Thus hydrothermal mineral deposits may occur at great distances from the sources of the solutions. Hydrothermal mineralisation is probably the single most important source of economic mineral deposits. Faults are planes of fracture in rocks along which the rocks on one side of the fracture have moved relative to the other.
Joints are also planes of fracture, but where there is no relative movement of the rocks.