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| G gabbro A dark, coarse-grained intrusive igneous rock. Gabbro is made of calcium-rich plagioclase, with amphibole and/or pyroxene, and is chemically equivalent to basalt.
Family of silicate minerals containing varying amounts of aluminum, iron, magnesium, and calcium. Schist and gneiss often have tiny, glassy red garnet dodecahedrons.
A branch of geology that focuses on the chemical composition of Earth materials.
Power generation using natural steam derived from the Earth’s internal heat. geomorphology A branch of geology and geography that studies the development of landforms.
Natural glass (obsidian) that forms when molten lava cools too rapidly to permit crystal growth. glacier A long-lived sheet or mass
of ice made of recrystallized snow. Glaciers move downhill due to the
stress of their own weight.
A coarse-grained, foliated metamorphic rock that commonly has alternating bands of light and dark-colored minerals. Gondwana A continent formed in the
Southern Hemisphere during the Late Paleozoic. It included most of South
America, Africa, India, Austrailia, and Antarctica.
An elongate block of rock down-dropped along roughly parallel faults. graded bed A sediment layer with a gradation of grain size from large grains to finer grains. grain size Refers to the size of individual mineral crystals or particles within a rock or sediment deposit.
A coarse-grained intrusive
igneous rock with at least 65% silica. Quartz, plagioclase feldspar
and potassium feldspar make up most of the rock and give it a fairly
light color. Granite has more potassium feldspar than plagioclase feldspar.
Usually with biotite, but also may have hornblende.
A general term for intrusive
igneous rocks that look similar to granite but may range in composition
from quartz-diorite to granite. All granitic rocks are light colored;
feldspar and quartz are visible in hand specimen.
An intrusive igneous rock
similar to granite, but contains more plagioclase than potassium feldspar.
All sedimentary particles
larger than two millimeters is called gravel. Gravel is subdivided into
pebbles, cobbles, and boulders.
A metamorphic rock derived from basalt or chemically equivalent rock such as gabbro. Greenstones contain sodium-rich plagioclase feldspar, chlorite, and epidote, as well as quartz. The chlorite and epidote make greenstones green.
Water found beneath the Earth’s surface where all empty space in the rock is completely filled with water.
Coarse sand and gravel that
forms from weathering of granitic rocks
A very small channel formed by running water. Gullies hold water for brief periods of time after a rain storm or snow melt. |
| H
The time required for one-half
of the atoms of a radioactive substance to decay.
A measure of a mineral’s resistance to scratching. The hardness of a mineral is measured by scratching it against another substance of known hardness. headland Headlands are projections
of land that stick out into a sea or lake.
An epoch of the Quaternary
Period beginning 10,000 years ago and continuing today.
An elongate block of rock uplifted along roughly parallel faults. hornblende See amphibole.
A schist rich in hornblende. Generally with abundant plagioclase feldspar as well. Grades into amphibolite. hornfels A dark, very fine-grained metamorphic rock produced by the recrystallization of a fine-grained rock by heat from a nearby igneous intrusion. From the German, meaning horn rock.
An area of concentrated heat in the mantle that produces magma that rises to the Earth’s surface to form volcanic islands. The volcanic activity of the Hawaiian Islands is one example. Hot spots generally persist for millions of years. hydrology The science that deals with water on and beneath the Earth surface.
Literally, "with water".
Refers to minerals or other materials which have water as a primary
constituent. |
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