Granite Light colored, coarse grained, intrusive rock with a felsic (silica-rich) composition that is mostly made of quartz, sodium and potassium-bearing feldspar, and plagioclase. Minor...

Granitoid A generic term referring to hard, coarsely crystalline plutonic rock that is produced by intrusion of magma followed by a long period of slow cooling and solidification below the...

Felsic A geological term referring to igneous rocks that are equivalent to rhyolite and granite in composition.

Heat Exchanger A system by which heat is transferred from one media (solid or fluid) to another with applications in heating and cooling. They are used in geothermal binary power plants and...

Heat exchanger A device or engineered system that is used to transfer thermal energy in soil, rock or produced fluid to heat a closed loop through which another fluid is circulated. Heat...

Hot Dry Rock Hot crystalline rock with essentially no porosity and lacking producible hot water. Geothermal production from hot dry rock reservoirs is the primary goal of EGS (enhanced...

Hydraulic Fracture A rock-hosted tensile fracture that is created by injection of fluid under high pressure.

Hydraulic Gradient The slope on the water table which promotes horizontal fluid flow in permeable rock units.

Hydrothermal Eruption Rare explosive discharge of hot water and steam that is powerful enough to excavate a crater and lift rock fragments and its pulverized equivalents into the air to...

Helium Isotopes Helium gas is a trace constituent of groundwater and thermal fluids, and the ratio of 3He to 4He can be measured with a high-precision mass spectrometer to determine whether...