Asthenosphere
The area of mantle, beneath the lithosphere, that is solid, but hotter than the rock above it and can flow under pressure; functions as a soft, weak zone over which the lithosphere may move. (1.3)
Continental rift
A low trough or series of troughs bounded by normal faults, especially where two parts of a continent begin to rift apart. (3.5)
Continental shelf
A gently sloping, shallow area of the ocean floor that extends outward from the edge of a continent
Convection cell
The movement of material in an elliptical to roughly circular loop by the process of convection; movement is driven by differences in den- sity, especially those caused by temperature variations. (5.4)
Convergent boundary
A plate-tectonic boundary in which two plates move toward (converge) relative to one another. (3.4)
Core
The central or innermost portion of the Earth, lying below the mantle and probably consisting of iron and nickel. It is divided into a liquid outer core, which begins at a depth of 2,898 km (1,800 mi), and a solid inner core, which begins at a depth of 4,
Divergent boundary
A plate-tectonic boundary in which two plates move
apart (diverge) relative to one another. (3.4)
Lithosphere
Earth's upper, rigid layer composed of the crust and uppermost mantle. (1.7)
Mantle
The most voluminous layer of Earth; located below the crust and above the core. (1.3)
Mantle plume
A posited thermal abnormality where hot rock nucleates at the core-mantle boundary and rises through the Earth's mantle becoming a diapir in the Earth's crust.
Magnetic anomaly
a departure from the normal magnetic field of the earth.
Magnetic reversals
A reversal of the polarity of Earth's magnetic field, from normal polarity to reversed polarity. (3.9)
Mid-ocean ridges
A long mountain range on the floor of the ocean, associated with seafloor spreading. (3.1)
Passive margin
A continental margin that is not a plate boundary. (3.5)
Plate tectonics
A theory in which the lithosphere is divided into a number of mostly rigid plates that move relative to one another, causing tectonic activity
along these boundaries. (3.4)
Gravitational sliding
Extensive sliding of strata down a slope of an uplifted area. Also known as sliding.
Rifting
A rift is a linear zone where the Earth's crust and lithosphere are being pulled apart
Slab-pull
A plate-driving force generated by the sinking action of a relatively dense, subducted slab. (3.8)
Sea-floor spreading
The process by which two oceanic plates move apart and
new magmatic material is added between the plates. (3.2)
Subduction
The process along a convergent plate-tectonic boundary in which an oceanic lithospheric plate descends beneath the overriding plate. (3.6)
Tectonic plate
The dozen or so fairly rigid blocks into which Earth's lithosphere is broken. (3.4)
Trenches
A narrow, steep-sided, elongate depression of the deep seafloor, formed by bending down of a subducting oceanic plate at a convergent plate bound-
ary; includes the deepest parts of the ocean. (3.1)
Volcanic island arcs
When either oceanic crust subducts under oceanic crust (oceanic arc) or continental crust subducts under continental crust (continental arc).
Amphibole
A group of silicate minerals, including hornblende, characterized by double chains of silicate tetrahedra; most common in igneous and metamor-
phic rocks. (4.6)
Biotite
typically black or brown mica (sheet silicate mineral). (4.8)
Calcite
A common rock-forming calcium carbonate mineral occurring in lime- stone and a variety of water-related deposits. (4.9)
Cleavage
The tendency of minerals to break along specific orientations of closely spaced planes (4.3). 2. The tendency of a rock, especially a metamor-phic rock, to split along mostly parallel planes. (8.6)
Conchoidal fracture
Describes the way that brittle materials break when they do not follow any natural planes of separation.
Crystal faces
The flat exterior surface of a crystal.
Element
A type of atom that has a specific number of protons and chemical characteristics. (4.6)
Garnet
A fairly common silicate mineral with a distinctive shape but nearly any color (red is most common). (4.8)
Gypsum
A common calcium sulfate mineral, generally formed by the evaporation of water. (4.9)
Graphite
A soft, black, greasy-feeling carbon mineral. (4.12)
Hardness
A mineral can be scratched by a mineral that is harder than the mineral, but not by one that is softer. (to estimate hardness we use scratch test, finger nail, penny, etc.)
Luster
he reflection of light from the surface of a mineral, especially its quality and intensity; the appearance of a mineral in reflected light. (4.3)
Mineral
A naturally occurring, inorganic, crystalline solid with a relatively consistent composition. (4.1)
Mohs hardness scale
Consists of ten common minerals ranked in order of
increasing relative hardness, from 1 to 10. (4.3)
Muscovite
A light-colored, sheet silicate mineral that is part of the mica family.
Olivine
A green iron-magnesium silicate mineral that composes much of the upper mantle and also occurs in mafic and ultramafic igneous rocks. (4.8)
Potassium feldspar
A very common silicate mineral that contains potassium; syn. K-feldspar. (4.8)
Pyroxene
One of a group of mostly dark, single-chain silicate minerals. (4.8)
Quartz
A very common rock-forming silicate mineral, consisting of crystalline silica. (4.8)
Rock
A naturally occurring solid mixture of one or more minerals or organic matter.
Silicate minerals
Minerals that contain silicon-oxygen tetrahedra; the most common min- eral group on Earth. (4.6)
Streak
The color of powder a mineral leaves when rubbed against a porcelain
plate. (4.3)
Talc
A very soft mineral that is a basic silicate of magnesium, has a soapy feel, and is used especially in making talcum powder.
Andesite
An intermediate-composition igneous rock that is the fine-grained equivalent of diorite; typically gray or greenish-gray, commonly with phenocrysts of cream-colored feldspar or dark amphibole. (5.2)
Aphanitic texture
Individual components can not be identified with the unaided eye.
Ash
The powdery residue left after the burning of a substance.
Assimilation
Assimilation assumes that a hot primitive melt intruding into a cooler, felsic crust will melt the crust and mix with the resulting melt. This then alters the composition of the primitive magma.
Basalt
A fine-grained, dark-colored mafic igneous rock, with or without vesicles and phenocrysts of pyroxene, olivine, or feldspar. (5.2)
Bowen's reaction series
An idealized sequence in which minerals could crys-
tallize from a magma as it cools. (5.8)
Decompression melting
Melting of a rock or other material due to a decrease in pressure. (5.5)
Diorite
A medium- to coarse-grained, intermediate-composition igneous rock; the phaneritic equivalent of andesite. (5.2)
Extrusive igneous rock
An igneous rock that forms when magma is erupted onto Earth's surface; syn. volcanic rock. (5.6)
Felsic
An igneous rock with a felsic composition, including granite, a light-colored igneous rock that contains abundant feldspar and quartz. (5.2)
Fractional crystallization
Is the removal and segregation from a melt of mineral precipitates, which changes the composition of the melt.
Geothermal
Energy derived from the heat in the interior of the earth
Geothermal gradient
The rate at which temperature increases with depth into
the subsurface. (5.4)
Glassy texture
Shiny texture (forms when lava flow cools to rapidly for crystallization).
Granite
A coarse-grained, felsic igneous rock containing mostly feldspar and quartz. (4.1)
Hot-spot volcanism
The creation of volcanoes on a planet's surface caused by a reservoir of hot magma in the planet's mantle under a thin part of the crust
Intermediate magma
If two different magmas come into contact, they may mix a process called magma mixing. Magma mixing produces a magma that has a composition intermediate between the two magmas that mixed.
Intrusive igneous rock
An igneous rock that solidified from magma below Earth's sur- face; syn. plutonic rock. (5.6)
Lahar
A mudflow mostly composed of volcanic-derived materials and generally formed on the flank of a volcano. (6.7)
Lava
Magma that is erupted onto the surface, or the rock mass into which it solidifies. (6.2)
Mafic
A material having high contents of magnesium (Mg) and iron (Fe), generally accompanied by a decreased amount of silica. (5.3)
Magma
Molten rock, which may or may not contain some crystals, solidified rock, and gas. (1.5)
Partial melting
When only the low-melting-temperature minerals melt in a rock.
Pegmatitic texture
An igneous rock containing very large crystals, which may be centimeters to meters long. (5.1)
Peridotite
An ultramafic igneous rock generally containing abundant olivine, commonly with smaller amounts of pyroxene. (5.2)
Phaneritic texture
An igneous rock containing crystals that are visible to the unaided eye. (5.1)
Porphyritic texture
An igneous texture in which larger crystals are set in a finer grained matrix. (18.11) porphyry A porphyritic igneous rock that contains conspicuous phenocrysts in a fine-grained matrix. (18.11)
Pyroclastic texture
Shows a mixture of rock fragments, pumice, and volcanic ash. The ash is very fine grained, so only the rock fragments and pumice are identifiable.
Rhyolite
A mostly fine-grained, felsic igneous rock, generally of volcanic origin; can contain glass, volcanic ash, pieces of pumice, and variable amounts of vis-
ible crystals (phenocrysts). (5.2)
Tuff
Volcanic rock composed of consolidated volcanic ash and other tephra, commonly including pumice, crystals, and rock fragments. (5.3)
Ultramafic
A generally dark or greenish igneous rock composed chiefly of mafic minerals rich in magnesium and iron. (5.2)
Viscosity
A measure of a material's resistance to flow. (5.7)
Volatiles
A chemical component that readily converts to a vapor phase under the proper conditions. (18.3)
Acid rain
Is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions (low pH).
Active volcano
Volcano could erupt at any moment. High risk for people that live in the area.
Aerosols
Very small solid particles or drops of liquid dispersed in the atmosphere. (6.6)
Albedo
The ratio of the amount of electromagnetic energy reflected by a surface to the amount of energy incident upon it. (14.8)
Caldera
A large volcanic depression that is typically circular to elongate in shape and formed by collapse of a magma chamber. (6.10)
Carbon dioxide
Volcanic base released with a basaltic eruption. Cause asphyxiation if concentrated. (The condition of being deprived of oxygen).
Composite volcano
A common type of volcano constructed of alternating layers of lava, pyroclastic deposits, and mass-wasting deposits, including mudflows; syn. stratovolcano. (6.7)
Mount St. Helens
1980 sleeping volcano erupted violently. The eruption formed a huge crater and a lava dome.
Mount Vesuvius
Active composite volcano near the city of Naples, Italy. In A.D 79, a series of pyroclastic flows moved down the flank on the volcano, destroying the coastal towns of Pompeii and Herculaneum and killed the cities inhabitants, about 20,000 people and 5,000
Pompeii
Coastal town that was destroyed by Mount Vesuvius eruption of pyroclastic flow.
Pyroclastic flow
A fast-moving cloud of hot volcanic gases, ash, pumice, and rock fragments that generally travel down the flanks of a volcano; syn. ash flow. (5.1)
Ring of fire
Is an area where a large number of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean.
Shield volcano
A type of volcano that has broad, gently curved slopes con- structed mostly of relatively fluid basaltic lava flows. (6.4)
Stratovolcano
A common type of volcano constructed of alternating layers of lava, pyroclastic deposits, and mass-wasting deposits, including mudflows; syn. composite volcano (6.7)
Sulfur dioxide
When expelled during eruptions can destroy crops, kill livestock, poison drinking water for people and animals.
Volcanic ash
Particles of volcanic tephra that are sand-sized or smaller, and accumulations of such material. (5.1)