N and O Index Glossary geology Science
N and O Index Glossary geology Science
Nannofossils
A generic term used in reference to very small fossils that are at the limit of resolution by a light microscope. They are therefore studied with electron microscopes and are frequently fossil discoasters and coccoliths.
Nappe
A large slab of earth's surface that has been moved in a horizontal or near horizontal direction over a plane of separation. This motion can be produced by faulting or sliding. The term is generally used for very large slabs which are many square kilometers or miles in surface area.
Native Metal
A natural deposit of a metallic element such as gold, silver, copper or iron in a pure form.
Natural Gas
Naturally occurring hydrocarbons that exist in subsurface rock units in the gaseous state. Methane is the most abundant but ethane, propane and others also occur.
Natural Levee
A mound of sediment that parallels a stream channel forming a levee-like deposit. When flood waters leave the normal stream channel and enter the flood plain there is a reduction of velocity that causes suspended sediments to fall to the bottom, producing this deposit.
Neap tide
A daily tidal range of minimal amplitude that occurs when the moon and sun are positioned at 90 degrees to one another. In this moon-earth-sun configuration, the gravitational attraction of the moon and sun compete for Earth's water. Occurs at the first and third quarters of the moon. See spring tide for contrast.
Nebula
A cloud of interstellar dust that is faintly visible from Earth.
Nebular hypothesis
A theory of the formation of the planets that states that a rotating nebula contracted and was then torn into fragments by centrifugal forces, with planets condensing from the fragments.
Neutron-activation analysis
A method of identifying isotopes of an element by bombarding them with neutrons and observing the characteristic radioactive decay products emitted.
natural bridge
An arch-shaped stretch of bedrock remaining in a karst region when the surrounding bedrock has dissolved.
natural spring
A place where groundwater flows to the surface and issues freely from the ground.
neutron
A particle that is found in the nucleus of an atom, has a mass approximately equal to that of a proton, and has no electric charge
nonfoliated
Being a metamorphic rock that does not show foliation.
normal fault
A dip-slip fault marked by a generally steep dip along which the hanging wall has moved downward relative to the foot wall.
nuclear fission
The division of the nuclei of isotopes of certain heavy elements, such as uranium and plutonium, effected by bombardment with neutrons. Nuclear fission causes the release of energy, additional neutrons, and an enormous quantity of heat. Nuclear fission is used in nuclear power plants and nuclear weapons. A byproduct of nuclear fission is toxic radioactive waste. See also nuclear fusion.
nucleus
The central part of an atom, containing most of the atom's mass and having a positive charge due to the presence of protons.
nuee ardente
A sometimes glowing cloud of gas and pyroclastics erupted from a volcano and moving swiftly down its slopes. Also called a pyroclastic flow.
Nodule
A mineral mass that has a different composition or is more weathering resistant than its surrounding rock. These are normally rounded in shape. Examples include chert masses in a limestone rock unit, pyrite masses in a coal seam, or carbonate masses in a shale. In most cases these "nodules" have formed within the rock unit or its former sediment mass. The term is also applied to rounded masses of manganese minerals that occur on some parts of the ocean floor.
nephelometric turbidity unit
(NTU)-unit of measure for the turbidity of water. Essentially, a measure of the cloudiness of water as measured by a nephelometer. Turbidity is based on the amount of light that is reflected off particles in the water.
The northeastern
Nuclear Family
Nodal Region
A region characterized by a set of places connected to another place by lines of communication or movement.Nodal Region
Nuclear Family
See Extended Family.
Pollution that does not originate at a single location. In an urban area runoff water can be polluted as it flows to a stream by gasoline, antifreeze, road salt or other contaminants. In rural areas runoff can be contaminated by insecticides, manure, or fertilizer. This contamination can be significant but can not be traced back to a specific source.
nuclear fusion
The combination of the nuclei of certain extremely light elements, especially hydrogen, effected by the application of high temperature and pressure. Nuclear fusion causes the release of an enormous amount of heat energy, comparable to that released by nuclear fission. The principal by product of nuclear fusion is helium.
numerical dating
The fixing of a geological structure or event in time, as by counting tree rings
Normal Fault
A fault with vertical movement and an inclined fault plane. The block above the fault has moved down relative to the block below the fault.
Oblique-Slip Fault
A fault that has both horizontal and vertical elements of displacement.
ocean trench
A deep, linear, relatively narrow depression in the sea floor, formed by the subduction of oceanic plates.
octet rule
A scientific law stating that all atoms, except those of hydrogen and helium, require eight electrons in the outermost energy level in order to maintain chemical stability.
oil sand
A mixture of unconsolidated sand and clay that contains a semi-solid bitumen.
ore
A mineral deposit that can be mined for a profit.
oblique slip
Fault motion that involves both dip-slip and strike-slip movement of fault blocks.
octet
rule A scientific law stating that all atoms, except those of hydrogen and helium, require eight electrons in the outermost energy level to maintain chemical stability.
orogenesis
Mountain formation, as caused by volcanism, subduction, plate divergence, folding, or the movement of fault blocks. Also called orogeny.
oscillatory motion
The circular movement of water up and down, with little or no change in position, as a wave passes.
Outwash
Sorted and stratified sediment deposited in front of a glacier by meltwater streams.
-A load of sediment, consisting of sand and gravel, that is deposited by meltwater in front of a glacier.
oxbow lake
A crescent-shaped body of standing water formed from a single loop that was cut off from a meandering stream, typically by a flood that allowed the stream to flow through its flood plain and bypass the loop.
oxidation
The process of combining with oxygen ions. A mineral that is exposed to air may undergo oxidation as a form of chemical weathering.
oxide
One of several minerals containing negative oxygen ions bonded to one or more positive metallic ions.
ocean
The salt water surrounding the great land masses, and divided by the land masses into several distinct portions, each of which is called an ocean.
A cattle- or sheep-ranching area characterized by a general absence of fences.
Orographic Rainfall
Precipitation that results when moist air is lifted over a topographic barrier such as a mountain range.
Overburden
Material covering a mineral seam or bed that must be removed before the mineral can be removed in strip mining.
Obsidian
A glassy igneous rock with a composition similar to granite. The glassy texture is a result of cooling so fast that mineral lattices were not developed.
Oil Field
The geographic area above an underground accumulation of oil and natural gas.
Oil Shale
A dark-colored shale containing an unusual amount of solid organic material. This shale can be crushed and heated to liberate gaseous and liquid hydrocarbons. At present the expenditure required to process oil shale into a fuel makes this effort marginally profitable or unprofitable.
Old Age
A stage in the development of a landscape when streams have a low gradient and meander back and forth across broad floodplains. The landscape is marked by meander scars and oxbow lakes.
Oolite
A small sphere of calcium carbonate no more than a few millimeters in diameter and with a concentric internal structure . These spheres are thought to have formed by inorganic precipitation of calcium carbonate in very thin layers around a grain of sand or a particle of shell or coral. A rock composed primarily of oolites.
Oolitic
A limestone texture that is characterized by spherical grains of calcium carbonate with a concentric internal structure. These grains are thought to form by inorganic precipitation of calcium carbonate around a sand grain or shell particle nucleus.
Octahedral coordination
The packing of six ions around an ion of opposite charge to form an octahedron.
Opaque mineral
A mineral which transmits no light through a thin section under a microscope. Usually a native metal, sulfide, or metallic oxide mineral.
Orbit
The elliptical or hyperbolic path traced by a planet or meteorite or satellite in the presence of a more massive body.
Oscillation ripple
A ripple with a symmetrical cross section and a sharp peak formed by waves.
Oxidized element
An element occurring in the more positively charged of two common ionic forms.
Opaque
An adjective used in reference to a substance that does not allow light of visible wavelength to enter or pass through. Minerals with a metallic or submetallic luster are normally opaque.
Ophiolite Suite
The typical sequence of rocks in the oceanic crust from bottom to top ultrabasic rocks, gabbro, sheeted dikes, pillow basalts, and sea-floor sediments. Igneous rocks and deep-sea sediments associated with divergence zones and the sea-floor environment.
organic matter
plant and animal residues, or substances made by living organisms. All are based upon carbon compounds.
osmosis
the movement of water molecules through a thin membrane. The osmosis process occurs in our bodies and is also one method of desalinizing saline water.
outfall
the place where a sewer, drain, or stream discharges; the outlet or structure through which reclaimed water or treated effluent is finally discharged to a receiving water body.
oxygen demand
the need for molecular oxygen to meet the needs of biological and chemical processes in water. Even though very little oxygen will dissolve in water, it is extremely important in biological and chemical processes.
Orbit
An elliptical or hyperbolic path traveled by a satellite object around a more massive body. For example, the Earth orbits the Sun.
A natural accumulation of a metal, gemstone or other valuable mineral substance, which is rich enough in concentration that it can be mined and processed at a profit.
A mineral that contains a high enough concentration of a useful element or compound that the element or compound can be extracted at a profit.
Original Horizontality
One of the principles of relative dating. Based upon the good assumption that sedimentary rocks are deposited in horizontal or nearly horizontal layers; then if sedimentary layers are found in an inclined orientation the force that moved them to that orientation must have been applied at some time after their deposition.
Orogenic Belt
A linear or arcuate region of folded and uplifted rocks.
Orogeny
A compressive tectonic process that results in intense folding, reverse faulting, crustal thickening, uplift and deep plutonic activity. A mountain-building episode.
Oscillation Ripple Marks
Symmetrical ridges in sand or other sediment that are caused by a back-and-forth wave action.
Outcrop
An exposure of bedrock. Outcrops can be formed naturally or by human action. Stream erosion and highway construction can produce outcrops.
Outgassing
The release of juvenile gases and water to the surface from a magma source.
Overturned Fold
A fold that has both limbs dipping in the same direction, resulting from one of those limbs being rotated through an angle of at least 90 degrees. Overturned folds are found in areas of intense deformation. The name overturned is given because the strata on one limb of the fold are "overturned" or upside down.