Dolomite A carbonate mineral similar to calcite in which magnesium partially substitutes for calcium.

Diorite Dark colored, coarse grained, intrusive rock that contains less silica than granite and that is mostly made of plagioclase, biotite, hornblende, pyroxene, and minor to nil quartz.

Epidote Alumino-silicate hydrothermal mineral having a distinctive yellow-green color that is used a mineral geothermometer, forming at temperatures above ~230°C. The first down hole...

Flowback Return flow of slickwater that was injected during a stimulation. This is a highly controlled process in which well head pressure is reduced to allow managed fluid recovery. Fluids...

Fumarole A steam vent and surface thermal feature that is commonly associated with steaming ground and mud pots in hydrothermally and volcanically active areas.

Geyser A rare type of hot spring that periodically discharges a fountain of hot water and steam (or sometimes just gas).

Geothermal Gradient The increase in temperature with depth below the surface, usually reported in units of °C/km.

Geochemical Tracer An environmentally benign chemical that is injected to trace fluid movement through the geothermal reservoir and that can be easily detected in produced hot fluid.

Gneiss Metamorphic rock that forms under intense pressure and high temperature and that is made of quartz, feldspar, amphibole and mica. Gneiss represents the highest grade of metamorphic...