A more efficient utilization of geothermal energy by allowing flashing of the produced water to a lower temperature. This is accomplished by causing additional quantities of silica to precipitate out of the geothermal water as particles rather than as scale on process equipment. These particles are tertiary aggregate amorphous silica of Type I, II or III, which have high surface areas, good oil absorption and high reflectivity. They are useful as additives and opacifiers for paper, paints, rubbers, and plastics; as thixotropic thickening agents; and as absorbents. The improved energy recovery is accomplished by utilizing the addition (including recycle) of previously produced particles of amorphous tertiary aggregate silica of a selected Type I, II or III, as a heterogeneous precipitation agent, alone or in combination with other more conventional precipitation agents.