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

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...

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...