Before it became the world’s largest geothermal power-producing site, The Geysers was known as the “Gates to Hades,” drawing visitors with its healing waters, steam vents, and wild legends.
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 rock, which is characterized by alternating bands of dark and light-colored minerals, foliation (i.e., parallel alignment of planar minerals) and tight folding. This rock type is common at mid to deep levels of continental crust.
Geothermal Glossary
Word of the Week – Cement Bond Log
Cement Bond Log A geophysical well log that is obtained using a sonic-type tool on a wireline. The result helps to confirm the integrity of the hardened cement that was injected to form a bond between well casing and the adjacent rock formation.
Word of the Week – Chemical Geothermometer
Chemical Geothermometer A temperature that is calculated based on the chemical composition of a hydrothermal fluid and involves knowing a ratio (e.g., Na/K) or knowing the absolute concentration of a species (e.g., SiO2). Temperature is computed using a simple...
Word of the Week – Chlorite
Chlorite A micaceous mineral that is commonly green-colored, composed of iron and/or magnesium, and forms due to hydrothermal alteration of amphiboles, pyroxenes, and feldspars.