Proppant Sand-sized solid grains that are injected in a fluid suspension and used to hold open stimulated fractures in a geothermal reservoir.

Propylitic Alteration A term borrowed from studies of hydrothermal ore deposits that refers to an assemblage of secondary hydrothermal minerals which forms in igneous rocks. This assemblage...

Rhyolite Light colored fined grained volcanic rock composed of glass, quartz, K-feldspar and plagioclase, with relatively high silica (69-77 wt %). The composition reflects partial melting...