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Geological Terms Beginning With "S"



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Saltation

Saltation

The transport of sediment in short jumps and bounces above the stream bed or ground by a current that is not strong enough to hold the sediment in continuous suspension. (See suspension and traction for comparison.)

Sand Dollar

Sand Dollar

Sand dollars found on beaches today are remains of a group of animals that has lived in the oceans for millions of years. Their bodies are often agatized by nature and then found by people who polish them into gems.

Sandstone

Sandstone

A sedimentary rock composed of sand-sized particles (1/16 to 2 millimeters in diameter).

Sapphire

Sapphire

Sapphire is a gem variety of the mineral corundum. When it is reddish blue to violet-blue, it is known simply as "sapphire." Corundums of any other color (except red, which is ruby) are known as "fancy sapphires."

Sardonyx

Sardonyx

Sardonyx is a member of the chalcedony family. It is a banded agate that contains bands of bright red alternating with agate of other colors.

Scapolite

Scapolite

Scapolite is a metamorphic mineral that sometimes occurs in transparent gem-quality crystals that make beautiful faceted gems. Some specimens contain a silk that can produce a strong cat's eye.

crown

Scarp

A exposed face of soil above the head of a landslide. It is also an exposure of the slip plane or surface of rupture. Scarps are one of the first obvious and easy-to-recognize signs that a slide is in progress.

Schist

Schist

A metamorphic rock containing abundant particles of mica, characterized by strong foliation, and originating from a metamorphism in which directed pressure plays a significant role.

Schistosity

Schistosity

The parallel arrangement of platy or prismatic minerals in a rock that is caused by metamorphism in which directed pressure plays a significant role.

Scoria

Scoria

An igneous rock of basaltic composition and containing numerous vesicles caused by trapped gases.

Sea-Floor Spreading

Sea-Floor Spreading

The process that occurs at mid-ocean ridges in which convection currents below pull the plates apart and create new sea floor.

Seamount

Seamount

A mountain on the sea floor that has at least 1000 meters of local relief. Most seamounts are shield volcanoes. (See also Guyot.)

Sediment

Sediment

A loose, unconsolidated deposit of weathering debris, chemical precipitates or biological debris that accumulates on Earth's surface.

Sedimentary Rock

Sedimentary Rock

A rock formed from the accumulation and consolidation of sediment, usually in layered deposits.

Sedimentary Structure

Sedimentary Structure

A structure in a sedimentary rock that forms at or near the time of deposition and reveals information about the depositional environment. Examples include: ripple marks, cross-bedding, mud cracks, and graded bedding.

Sedimentation

Sedimentation

The process of sediment deposition from out of a suspension or solution.

Seepage

Seepage

The slow movement of water through the pore spaces of a solid material. This term is also applied to a loss of water by infiltration through the bottom of a stream, canal, irrigation ditch, reservoir or other body of water.

Seif Dune

Seif Dune

A large sand dune that forms parallel to the direction of a strong wind that blows in a consistent direction throughout the year. Also called a longitudinal dune.

Seismic Discontinuity

Seismic Discontinuity

A surface separating rocks that transmit seismic waves at different velocities.

Seismicity

Seismicity

The study of the worldwide distribution of earthquakes and crustal movement over time and the probability of an earthquake occurring in a specific location.

seismic wave

Seismic Wave

A generic term for the numerous types of waves that are produced by an earthquake and travel through the earth. Depending upon the intensity, depth and location of the earthquake these vibrations might or might not be felt at the surface by people.

seismogram

Seismogram

A paper, film or digital recording of an earthquake's vibrations that is produced by a seismograph.

seismograph

Seismograph

The study of the worldwide distribution of earthquakes over time and the probability of an earthquake occurring in a specific location.

Septarian

Septarian

"Septarian" is a name used for round concretions with internal mineral-filled fractures found in sedimentary rocks. They are often cut into cabochons that display the interesting geometry of the fracture network.

Seraphinite

Seraphinite

Seraphinite is a trade name used for a gem material composed of the mineral clinochlore. It is usually greenish in color and marked with fibrous or feather-like patterns. Its hardness is only 3 to 4 and is reserved for delicate use.

Serpentine

Serpentine

A silicate mineral, that occurs in a wide range of green and greenish colors with interesting patterns that is often cut into cabochons or used as an ornamental stone.

Service Well

Service Well

A well drilled to support production from other wells. Some reasons for support wells are: gas injection, water injection, steam injection, salt water disposal, water supply, observation, or combustion air injection.

Settling Pond

Settling Pond

An open pond where runoff, waste or process water is allowed to stand while suspended materials settle out. Settling ponds are common at surface mines, drilling sites, landfills, construction sites, industrial facilities and many other locations.

Shale

Shale

A clastic sedimentary rock that is made up of clay-size (less then 1/256 millimeter in diameter) weathering debris. It typically breaks into thin flat pieces.

shield volcano

Shield Volcano

A broad volcano with a very gentle slope that has been built up by many successive flows of low viscosity lava, usually of basaltic composition. The Hawaiian Islands are the best-know example of shield volcanoes.

Short Ton

Short Ton

A unit of weight that equals 2,000 pounds.

Shut In

Shut In

An oil or gas well that is capable of production but which is temporarily closed. The most common reason for a well to be "shut-in" is a lack of pipeline capacity or lack of access to markets. In some cases a lessee might drill a well to fulfill a lease commitment and then shut the well in until pipeline capacity or a favorable sales contract is available. This is often a strategy to lock-in the lease without additional cost. Shut-in wells can also be closed for maintenance. The image shows the map symbols for shut in oil wells (left) and gas wells (right).

Siderite

Siderite

Siderite is an iron carbonate mineral with a very high dispersion. Transparent crystals of siderite with great clarity can be cut into attractive gemstones with a strong fire. It is too soft for most jewelry and is a collector's stone.

Signing Bonus

Signing Bonus

Money paid to a mineral rights owner in exchange for granting a lease. This payment may be in addition to rental or royalty payments.

sill

Sill

A subsurface igneous rock body that is tabular in shape and has intruded between layers of the sedimentary or metamorphic country rock. A sill might branch off of a dike, a volcanic pipe or any other intrusive rock unit.

Sillimanite

Sillimanite

Sillimanite is a metamorphic mineral that often has a fine fibrous silk. When properly cut, cabochons of the material can reflect a sharp cat's eye.

Siltstone

Siltstone

A clastic sedimentary rock that forms from silt-size (between 1/256 and 1/16 millimeter diameter) weathering debris.

Silver

Silver

Silver is a precious metal that is often present as visible crystals in its ore. Some people enjoy seeing the bright metal reflecting from the surface of a cabochon. It is a novelty gem.

Sinkhole

Sinkhole

A depression in the land surface that results from the collapse or slow settlement of underground voids produced by solution weathering. The rock being dissolved is normally limestone but can also be salt, gypsum or dolostone. The photo shows a sinkhole that formed near Frederick, Maryland.

Slate

Slate

A foliated metamorphic rock that is formed through the metamorphism of shale. It is a low grade metamorphic rock that splits into thin pieces.

slip plane

Slip Plane

The surface of failure below a landslide (often called the "surface of rupture"). The moving mass of the slide travels over the slip plane.

slump

Slump

Also known as a "rotational slide". A slide in which the surface of rupture, or slip plane, is curved concave upward and the slide movement is roughly rotational instead of translational.

Smithsonite

Smithsonite

Smithsonite is a zinc carbonate mineral that serves as a minor ore of zinc and as a minor gem mineral. It is relatively soft and used as a collector's gem and in jewelry that is unlikely to receive abrasion or impact.

Smoky Quartz

Smoky Quartz

Smoky quartz is a grayish brown to nearly black variety of transparent quartz. It is often cut as a faceted stone or cabochon. Upon heating, it will sometimes change in color to yellow or yellowish brown citrine.

Sodalite

Sodalite

A feldspathoid mineral that ranges in color from white to blue to violet blue. It is often used to make cabochons, tumbled stones and other lapidary projects.

soft water

Soft Water

Water that does not contain significant amounts of dissolved calcium and magnesium ions that can interfere with the performance of many soaps and detergents. These dissolved substances are also not present to leave a scaly deposit in containers where it is heated or evaporates (although other dissolved substances might leave such deposits).

Solution

Solution

A chemical weathering process in which a material is dissolved. Also, the transport of dissolved ions by the water of a stream.

Spectrolite

Spectrolite

Some specimens of gem-quality labradorite have exceptional color and labradorescence. These unusual gems are given the name "spectrolite" because of the spectrum of colors that they reflect

Spessartine Garnet

Spessartine Garnet

Spessartine is also known as "spessartite" or as "mandarin garnet" because of its yellow-orange to orange-red color. It is a popular variety of garnet used in jewelry.

Sphene

Sphene

Sphene, also known as titanite, is a gem with a dispersion higher than diamond. Specimens of high clarity can be cut into gems with a brilliant fire. Its softness limits its use to earrings, pins, pendants, and low-abrasion jewelry pieces.

Spinel

Spinel

A mineral of many colors that has been treasured as a gem for thousands of years. It was often confused with ruby and sapphire. Many of these errors were not discovered until the 20th century

Spring Tide

Spring Tide

A daily tidal range of maximum amplitude that occurs when the earth, moon and sun are in alignment with one another. In this moon-earth-sun configuration, the gravitational attraction of the moon and sun work together to pull Earth's water into two bulges on opposite sides of the Earth. Occurs at the second and fourth quarters of the moon. See neap tide for contrast.

Star Dunes

Star Dunes

Radial shaped sand dunes with three or more arms. They form in areas where there is no dominant wind direction and wind blows from many different directions. They tend to accumulate upwards instead of moving laterally. This enables them to become some of the tallest dunes in the world.

Storm Sewer

Storage Well

A well where natural gas, crude oil, helium or another fluid is injected into temporary underground storage. In some areas the winter demand for natural gas for space heating is enormous but the pipeline capacity into that area is limited. So, all summer, natural gas will flow in from the producing area, injected underground and then withdrawn during the winter heating system. The image is the map symbol for a natural gas storage well.

Storm Sewer

Storm Sewer

A sewer system that collects surface runoff instead of waste water. These two types of water are kept separate because they require different processing before release to the environment.

Storm Surge

Storm Surge

The piling up of water along a shoreline cause by the sustained winds of a strong storm - usually a hurricane.

Strain

Strain

A change in the volume or shape of a rock mass in response to stress.

strata

Strata

A generalized term used in reference to a group of rock layers. "Strata" when plural, "stratum" when singular. These layers can be distinguished from layers above them and below them by differences in mineral composition, grain size, color, fossil content, grain orientation or other characteristic. The image is from William Smith's 1815 Geological Map of England and Wales and Part of Scotland.

indurated tuff

Stratification

A layered structure of sedimentary and other types of rocks in which the individual layers can be recognized and traced laterally because they differ in composition, color, grain size, fossil content, grain orientation or other observable characteristic.

indurated tuff

Stratified

A material that has been deposited in layers. Many types of processes can produce stratified deposits. These include: clastic sedimentation, chemical sedimentation, biological sedimentation, ash falls, lava flows, pyroclastic flows, landslides, asteroid impacts and others. Shown in the image is a sequence of stratified tuff accumulated near the Mount St. Helens eruption.

Stratigraphic Column

Stratigraphic Column

A diagram that shows the vertical sequence of rock units present beneath a given location with the oldest at the bottom and youngest at the top. They are typically drawn to approximate scale with proportional rock unit thicknesses. Colors and standardized symbols are usually added to graphically communicate rock types and some of their more important features. Geologic columns prepared for regions will have generalized thicknesses and rock unit features that show relationships that change over distance.

Stratigraphic Sequence

Stratigraphic Sequence

The sequence of sedimentary rock layers found in a specific geographic area, arranged in the order of their deposition.

Stratigraphy

Stratigraphy

The study of sedimentary rock units, including their geographic extent, age, classification, characteristics and formation.

Composite Cone

Stratovolcano

A volcanic cone made up of alternating layers of lava flows and pyroclastics. Also known as a composite cone. Most of the volcanoes in the Cascades Range are stratovolcanoes.

Streak

Streak

The color of a mineral in powdered form. Streak is normally determined by scraping a specimen across a surface of unglazed porcelain known as a "streak plate".

Streak Plate

Streak Plate

A piece of unglazed porcelain that is used for determining the streak of a mineral specimen.

Stream Order

Stream Order

A classification system that represents the relative position of streams in a drainage basin. The highest tributaries in the basin are first order streams. These converge to form second order streams, which have only first order streams as their tributaries. Third order streams form by the confluence of two second order streams. The numbering system continues downstream resulting in higher stream orders.

Stress

Stress

A force acting upon or within a mass or rock, expressed in terms of unit weight per surface area such as tons per square inch.

Striations

Striations

Scratches or grooves on a rock or sediment surface caused by abrasive action of objects being transported above it by ice, water or wind.

Strike

Strike

The geographic direction of a line created by the intersection of a plane and the horizontal. Often used to describe the geographic "trend" of a fold or fault.

Strike-Slip Fault

Strike-Slip Fault

A fault with horizontal displacement. Strike-slip faults are typically vertical or near vertical and are typically caused by shear stress. They are the typical fault of transform plate boundaries. The San Andreas Fault is the world's most famous example of a strike-slip fault.

Stromatolite

Stromatolite

A mound-shaped fossil that forms from the repetitious layering of algal mat covered by trapped sediment particles.

Strombolian Eruption

Strombolian Eruption

A type of volcanic eruption characterized by fountains of lava jetting from a lava-filled central crater.

Subduction Zone

Subduction Zone

An area at a convergent plate boundary where an oceanic plate is being forced down into the mantle beneath another plate. These can be identified by a zone of progressively deeper earthquakes.

Sublimation

Sublimation

The process by which a solid is deposited directly from a gas without going through a liquid phase. Sublimation frequently occurs around volcanic vents where minerals such as sulfur, orpiment, realgar and cinnabar are deposited. Even minerals like beryl can be deposited directly from hot gases in hydrothermal veins. These specimens are often of great purity because the crystals grew by the direct deposition of atoms.

Submarine Canyon

Submarine Canyon

An underwater canyon, carved into the continental shelf. These can be carved by turbidity currents or carved subaerially during a time when sea level was lower.

Subsidence

Subsidence

A lowering of the land surface in response to subsurface weathering, collapse or slow settlement of underground mines, or the production of subsurface fluids such as ground water or oil. The photo shows a sinkhole that formed near Frederick, Maryland.

Sugilite

Sugilite

Sugilite is a rare silicate mineral only discovered in 1994. It occurs in yellow, brown, pink and purple and is often combined with quartz. The purple color has become very popular in the lapidary trade. Its high price limits its popularity.

Sunstone

Sunstone

A plagioclase feldspar that can be a colorful transparent gem. It can also contain plate-shaped copper inclusions that produce an aventurescent flash when moved under incident light. These specimens are from Oregon.

Supercontinent

Supercontinent

A large landmass that forms from the convergence of multiple continents.

Superposed Stream

Superposed Stream

A stream that cuts across resistant bedrock units. This can occur when the stream's course was determined at a previous time and on a previous landscape.

Superposition

Superposition

The concept that the oldest rock layers are at the bottom of a sequence with younger rock layers deposited on top of them. This can be considered a rule that applies in all situations, except where the rocks are extremely deformed.

Supersaturated Solution

Supersaturated Solution

A solution that contains more solute than its solubility allows. Such a solution is unstable and precipitation can be triggered by a variety of events.

Surf

Surf

The breaking of waves as they enter shallow water.

Surf Zone

Surf Zone

An area of breaking waves bounded by the point of first breakers, then landward to the maximum uprush of waves on the beach.

Surface rupture

Surface Rupture

The location where the displacement of a fault cuts the Earth's surface. Because the surface is usually covered with soil or other loose material, the rupture may be an "area of disturbance" rather than a clean break.

Surface Wave

Surface Wave

A type of seismic wave that travels along Earth's surface. These are the waves that cause the most damage during an earthquake.

Suspended Load

Suspended Load

Small particles being carried by a stream and held in suspension by the movement of the water. The blizzard of tiny particles in the image represent the suspended load of a stream. They contrast with the larger particles of bedload on the bottom of the stream and the dissolved load of ions represented as the "+" and "-" symbols in the enlargement. Many streams only have a suspended load during times of high flow. Most of the time the water in the stream is clear and moving at such a slow rate that particles are not held in suspension.

Suspension

Suspension

Transport of sediment by wind or water currents that are strong enough to keep the sediment particles continuously above the stream bottom or ground.

Swash

Swash

The rush of a breaking wave up the slope of a beach.

Surface Wave

S-wave

Secondary seismic waves. A seismic wave with a direction of vibration that is perpendicular to the direction of travel. S-waves are slower than P-waves and travel only through solids.

Symbiosis

Symbiosis

A relationship between two species who live in close association but do not compete with each other or prey on one another. At least one of the species derives benefit from this association.

Syncline

Syncline

A trough-shaped fold with youngest strata in the center. Sketch by Sir Charles Lyell.

System

System

A stratigraphic unit of major significance which was deposited during a specific time period, and which can be correlated worldwide on the basis of its fossil content.

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