Geology of National Parks
Terms
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- Mica group
- Group of minerals with a sheet-silicate structure.
- Half-life
- The time it takes for a given amount of a radioactive isotope to be reduced by one-half. 1:1, 3:1, 7:1, 15:1, 31:1
- Cenozoic Era
- The most recent of the eras; followed the Mesozoic Era.
- Olivine
- A ferromagnesian mineral with the formula (Fe, Mg)2SiO4. Common in Peridotite.
- Transgression
- Sea level rises (comes toward land).
- Magma
- Molten rock, usually mostly silica. The liquid may contain dissolved gases as well as some solid minerals.
- Precambrian
- The vast amount of time that preceded the Paleozoic Era.
- Lithosphere
- The rigid outer shell of Earth, 70 to 125 or more kilometers thick.
- Diorite
- Coarse-grained igneous rock of intermediate composition. Up to half of the rock is plagioclase feldspar and the rest is ferromagnesian minerals.
- Shale
- A fine-grained sedimentary rock (grains finer than 1/16 millimeter in diameter) formed by the cementation of silt and clay (mud). Has thin layers (laminations) and an ability to split (fissility) into small chips.
- Weathering
- The group of processes that change rock at or near Earth's surface.
- Plate tectonics
- A theory that Earth's surface is divided into a few large thick plates that are slowly moving and changing in size. Intense geologic activity occurs at the plate boundaries.
- Pressure release
- A significant type of mechanical weathering that causes rocks to crack when overburden is removed.
- Obsidian
- Volcanic glass.
- Geyser
- Type of hot spring that erupts periodically, ejecting a column of hot water and steam into the air.
- Intrusive rock (plutonic rock)
- Rock that appears to have crystallized from magma emplaced in surrounding rock.
- Isolated silicate structure
- Silicate minerals that are structure so that none of the oxygen atoms are shared by silica tetrahedrons.
- Rounding
- The grinding away of sharp edges and corners of rock fragments during transportation.
- Basalt
- A fine-grained, mafic, igneous rock composed predominantly of ferromagnesian minerals and with lesser amounts of calcium-rich plagioclase feldspar.
- Paleozoic Era
- The era that followed the Precambrian and began with the appearance of complex life, as indicated by fossils.
- Quartz
- Mineral with the formula SiO2. Common in Granite.
- Carbonation
- CO2+H20 -> CH2O3 (Carbonic Acid). Reacts with rocks and breaks them down.
- Feldspar
- Group of most common minerals of Earth's crust. All feldspars contain silicon, aluminum, and oxygen and may contain potassium, calcium, and sodium.
- Peridotite
- Ultramafic rock composed of pyroxene and olivine.
- Silicic (felsic) rock
- Silica-rich igneous rock or magma with a relatively high content of potassium and sodium.
- Volcanic dome
- A steep-sided, dome- or spine-shaped mass of volcanic rock formed from viscous lava that solidifies in or immediately above a volcanic vent.
- Chemical weathering
- The decomposition of rock resulting from exposure to water and atmospheric gases.
- Unconformity
- A surface that represents a break in the geologic record, with the rock unit immediately above it being considerable younger than the rock beneath.
- Cross-bedding
- An arrangement of relatively thin layers of rock inclined at an angle to the more nearly horizontal bedding planes of the larger rock unit.
- Crystalline
- Describing a substance in which the atoms are arranged in a regular, repeating, orderly pattern.
- Asthenosphere
- A region of Earth's outer shell beneath the lithosphere. The asthenosphere is of inderterminate thickness and behaves plastically.
- Uniformitarianism
- Principle that geologic processes operating at present are the same processes that operated in the past. The principle is stated more succinctly as, "The present is the key to the past."
- Deposition
- The settling or coming to rest of transported material.
- Viscosity
- Resistance to flow.
- Chemical sedimentary rock
- A rock composed of material precipitated directly from solution.
- Superposition
- A principle or law stating that within a sequence of undisturbed sedimentary rocks, the oldest layers are on the bottom, the youngest on the top.
- Shield Volcano
- Broad, gently sloping cone constructed of solidified lava flows.
- Mid-oceanic ridge
- A giant mountain range that lies under the ocean and extends around the world.
- Frost wedging
- A type of frost action in which the expansion of freezing water pries a rock apart.
- Lava
- Magma on Earth's surface.
- Partial melting
- Melting of the components of a rock with the lowest melting temperatures.
- Moho (Mohorovicic discontinuity)
- The boundary separating the crust from the mantle beneath it.
- Formation
- A body of rock of considerable thickness that has a recognizable unity or similarity making it distinguishable from adjacent rock units. Usually composed of one bed or several beds of sedimentary rock, although the term is also applied to units of metamorphic and igneous rock. A convenient unit for mapping, describing, or interpreting the geology of a region.
- Convergent plate boundary
- A boundary between two plates that are moving toward each other.
- Andesite
- Fine-grained igneous rock of intermediate composition. Up to half of the rock is plagioclase feldspar with the rest beingferromagnesian minerals.
- Ultramafic rock
- Rock composed entirely or almost entirely of ferromagnesian minerals.
- Sheet-silicate structure
- Crystal structure in which each silica tetrahedron shares three oxygen ions.
- Extrusive rock (volcanic)
- Any igneous rock that forms at Earth's surface, whether it solidifies directly from a lava flow or is pyroclastic.
- Correlation (rock or fossil)
- In geology, correlation usually means determining time equivalency of rock units. Rock units may be correlated within a region, a continent, and even between continents.
- Granite
- A felsic, coarse-grained, intrusive igneous rock containing quartz and composed mostly of potassium- and sodium-rich feldspars.
- Differential weathering
- Varying rates of weathering resulting from some rocks in an area being more resistant to weathering than others.
- Cross-cutting relationship
- A principle or law stating that a disrupted pattern is older than the cause of disruption.
- Limestone
- A sedimentary rock composed mostly of calcite.
- Core
- The central zone of Earth.
- Radioactive decay
- The spontaneous nuclear disintegration of certain isotopes.
- Lahar (mudflow)
- A flowing mixture of debris and water, usually moving down a channel.
- Mud crack
- Polygonal crack formed in very fine-grained sediment as it dries.
- Erosion
- The physical removal of rock by an agent such as running water, glacial ice, or wind.
- Sorting
- Process of selection and separation of sediment grains according to their grain size (or grain shape or specific gravity).
- Crust (oceanic and continental)
- The outer layer of rock, forming a thin skin over Earth's surface.
- Silica
- A term used for oxygen plus silicon.
- Regression
- Sea level lowers (heads away from land).
- Organic sedimentary rock
- Rock composed mostly of remains of plants and animals.
- Bedding
- An arrangement of layers or beds of rock.
- Mafic rock
- Silica-deficient igneous rock with a relatively high content of magnesium, iron, and calcium.
- Silicate
- A substance that contains silica as part of its chemical formula.
- Geothermal gradient
- Rate of temperature increase associated with increasing depth beneath the surface of Earth (normally about 25C per kilometer).
- Sedimentary structure
- A feature found within sedimentary rocks, usually formed during or shortly after deposition of the sediment and before lithification.
- Index fossil
- A fossil from a very short-lived speies known to have existed during a specific period of geologic time.
- Pyroclastic Flow
- Turbulent mixture of pyroclastics and gases flowing down the flank of a volcano.
- Framework silicate structure
- Crystal structure in which all four oxygen ions of a silica tetrahedron are shared by adjacent ions.
- Intermediate rock (magma)
- Rock with a chemical content between felsic and mafic compositions.
- Mesozoic Era
- The era the followed the Paleozoic Era and preceded the Cenozoic Era.
- Rift zone (valley)
- A tensional valley bounded by normal faults. Rift valleys are found at diverging plate boundaries on continents and along the crest of the mid-oceanic ridge.
- Frost heaving
- The lifting of rock or soil by the expansion of freezing water.
- Frost action
- Mechanical weathering of rock by freezing water.
- Silicon-oxygen tetrahedron
- Four-sided, pyramidal object that visually represents the four oxygen atoms surrounding a silicon atom; the basic building block of silicate minerals. Also called a silica tetrahedron or a silicon tetrahedron.
- Transform plate boundary
- Boundary between two plates that are sliding past each other.
- Caldera
- A volcanic depression much larger than the original crater.
- Sedimentary rock
- Rock that has formed from (1) lithification of any type of sediment, (2) precipitation from solution, or (3) consolidation of remains of plants or animals.
- Plate
- A large, mobile slab of rock making up part of Earth's surface.
- Convection
- A very slow circulation of a substance driven by differences in temperature and density within the substance.
- Cinder cone
- A volcano constructed of loose rock fragments ejected from a central vent.
- Exfoliation
- The stripping of concentric rock slabs from the outer surface of a rock mass.
- Mantle
- A thick shell of rock that separates Earth's crust above from the core below.
- Pyroxene group
- Mineral group, all members of which are single-chain silicates.
- Mechanical weathering
- The physical disintegration of rock into smaller pieces.
- Decompression melting
- Partial melting of hot mantle rock when it moves upward and the pressure is reduced to the extent that the melting point drops to the temperature of the body.
- Seafloor spreading
- The concept that the ocean floor is moving away from the mid-oceanic ridge and across the deep-ocean basin, the disappear beneath continents and island arcs.
- Mantle plume
- Narrow column of hot mantle rock that rises and spreads radially outward.
- Amphibolite
- Amphibole (hornblende), plagioclase schist.
- Mineral
- A crystalline substance that is naturally occurring and is chemically and physically distinctive.
- Isotopic Dating
- Determining the age of a rock or mineral through its radioactive elements and decay products.
- Relative time
- The sequence in which events took place (not measured in time units).
- Igneous rock
- A rock formed or apparently formed from solidification of magma.
- Divergent plate boundary
- Boundary separating two plates moving away from each other.
- Isotopes
- Atoms (of the same element) that have defferent numbers of neutrons but the same number of protons.
- Volcano
- A hill or mountain constructed by the extrusion of lava or rock fragments from a vent.
- Environment of deposition
- The location in which deposition occurs, usually marked by characteristic physical, chemical, or biological conditions.
- Subduction
- The sliding of the sea floor beneath a continent or island arc.
- Original horizontality
- The deposition of most water-laid sediment in horizontal or near-horizontal layers that are essentially parallel to the Earth's surface.
- Hotspot
- An area of volcanic eruptions and high heat flow above a rising mantle plume.
- Composite volcano (Stratovolcano)
- A volcano constructed of alternating layers of pyroclastics and rock solidified from lava flows.
- Sandstone
- A medium-grained sedimentary rock (grains between 1/16 and 2 millimeters) formed by the cementation of sand grains.
- Sediment
- Loose, solid particles that can originate by (1) weathering and erosion of preexisting rocks, (2) chemical precipitation from solution, usually in water, and (3) secretion by organisms.
- Chain silicate structure
- Silicate structure in which two of each tetrahedron's oxygen ions are shared with adjacent tetrahedrons, resulting in a chain of tetrahedrons.
- Ripple mark
- Any of the small ridges formed on sediment surfaces exposed to moving wind or water. The ridges form perpendicularly to the motion.
- Gabbro
- A mafic, coarse-grained igneous rock composed predominantly of ferromagnesian minerals and with lesser amounts of calcium-rich plagioclase feldspar.
- Navajo sandstone
- Zion NP, desert envioroment, sedimentary, White Cliffs.
- Rhyolite
- A fine-grained, felsic, igneous rock made up mostly of feldspar and quartz.