A group of aluminosilicate minerals commonly found in metamorphic rocks that contain varying amounts of Ca, Fe, Mg, and Mn. Garnet is used as a semiprecious stone and an abrasive.
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Glossary
Garnet
Geographic Information System (GIS)
A computer application used to store, view, and analyze geographical information, especially maps.
Geologic Map
A two-dimensional representation of the Earth’s surface on which is recorded geologic information, such as the distribution, nature, and age relationships of rock units and the occurrence of structural features, mineral deposits, and fossil localities.
Geomorphology
The study of the classification, description, nature, origin, and development of landforms and their relationships to underlying structures, and of the history of geologic changes as recorded by these surface features.
Gneiss
A foliated rock, usually formed by regional metamorphism, in which bands or layers of granular minerals alternate with bands or layers in which minerals having flaky or elongate prismatic habits predominate.
Granite
A common, light-colored, coarse-grained plutonic igneous rock consisting of variable amounts of quartz, feldspar, and accessory minerals.
Graupel
Soft hail or snow pellets.
Gravel
An unconsolidated, natural accumulation of rock fragments resulting from erosion and consisting predominantly of particles larger than sand but smaller than cobbles greater than 0.19 inches and smaller than 3 inches (ASTM 2487-85, 1985).
Graywacke
A typically light to dark grey, poorly-sorted sandstone in which coarser fragments of rocks and minerals are cemented together by fine-grained material, much of which consists of clay minerals.
Groundwater
Water below the surface of the Earth. Also spelled: ground water, ground-water.