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Elastic deformation Nonpermanent deformation in which rock returns to its original shape
when the stress is released.
Erosion The incorporation and transportation of material by a mobile agent, such as water, wind,
or ice.
Evaporite A sedimentary rock formed of material deposited from solution by evaporation of
water.
External process Process such as weathering, mass wasting, or erosion that is powered by the
Sun and transforms solid rock into sediment.
Extrusive Igneous activity that occurs at Earth’s surface.
F
Fault A break in a rock mass along which movement has occurred.
Felsic A term derived from feldspar and silica (quartz). It is a term used to describe granitic
igneous rocks.
Fissure A crack in rock along which there is a distinct separation.
Fissure eruption An eruption in which lava is extruded from narrow fractures or cracks in the
crust.
Flood The overflow of a stream channel that occurs when discharge exceeds the channel’s
capacity. The most common and destructive geologic hazard.
Flow A type of movement common to mass-wasting processes in which water-saturated material
moves downslope as a viscous fluid.
Fossil The remains or traces of organisms preserved from the geologic past.
Fracture (rock) Any break or rupture in rock along which no appreciable movement has taken
place.
Frost wedging The mechanical breakup of rock caused by the expansion of freezing water in
cracks and crevices.
G
Geology The science that examines Earth, its form and composition, and the changes it has
undergone and is undergoing.
Geosphere The solid Earth; one of Earth’s four basic spheres.
Glacier A thick mass of ice originating on land from the compaction and recrystallization of
snow. The ice shows evidence of past or present flow.
Glassy texture A term used to describe the texture of certain igneous rocks, such as obsidian,
that contain no crystals.
Granitic Igneous rocks composed mainly of light-colored silicates (quartz and feldspar) are said
to have this composition.
Groundwater Water in the zone of saturation.
H
Hardness A mineral’s resistance to scratching and abrasion.
Hydrologic cycle The unending circulation of Earth’s water supply. The cycle is powered by
energy from the Sun and is characterized by continuous exchanges of water among the oceans,
the atmosphere, and the continents.
Hydrosphere The water portion of our planet; one of the traditional subdivisions of Earth’s
physical environment.
Hydrothermal metamorphism Chemical alterations that occur as hot, ion-rich water circulates
through fractures in rock.
I
Ice sheet A very large, thick mass of glacial ice flowing outward in all directions from one or
more accumulation centers.
Igneous rock A rock formed by the crystallization of molten magma.
Inclusion A piece of one rock unit contained within another; inclusions are used in relative
dating. The rock mass adjacent to the one containing the inclusion must have been there first in
order to provide the fragment.