Glossary of Rock and Mineral Terms - S

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saccharroidal

Composed of tiny, equi-dimensional crystals that resemble grains of sugar.

saline

Containing salt.

saline deposit

Mineral environment containing minerals formed through partial or full evaporation of a mineral-rich, saline lake.

saline lake

Mineral-rich lake found in arid regions that contains a heavy salt content, and frequently contains evaporite minerals which form as the lake evaporates. Saline lakes may fully evaporate, in which they become dry lakes.

salinity

Amount of salt present.

salt

1) Compound formed when a metal partially or fully takes the place of hydrogen in an acid. 

2) The mineral Halite.

salt dome

Separated fold in an anticline which is plugged up with a mass of salt.

sand

Accumulation of small grains of rock, usually found at beaches and in desert regions.

sandstone

A clastic rock composed of particles that range in diameter from 1/16 millimeter to 2 millimeters in diameter. Sandstones make up about 25% of all sedimentary rocks.

scalenohedron

Six sided polyhedron, similar to a bipyramidal hexagon, but the adjoining area at the center is diagonal between every side as opposed to being level. Other modifications might be present. Minerals shape this way are scalenohedral.

scales

Aggregate of small, flattened, overlapping crystals, as seen in fish scales.

scaly

Describing an aggregate of scales.

scarp

The steep cliff face that is formed by a slump.

scepter

Crystal deformity where the top part of a prismatic crystal protrudes and is wider than the rest of the crystal.

schiller

Color reflections or color "flashes" present in a mineral. The individual color flashes of Opal are known as "schillers".

schist

A coarse-grained, strongly foliated metamorphic rock that develops from phyllite and splits easily into flat, parallel slabs. Type of metamorphic rock made up of parallel layers of flaky, micaceous minerals.

scientific law

1. A natural phenomenon that has been proven to occur invariably whenever certain conditions are met. 2. A formal statement describing such a phenomenon and the conditions under which it occurs. Also called law.

scientific methods

Techniques that involve gathering all available data on a subject, forming a hypothesis to explain the data, conducting experiments to test the hypothesis, and modifying or confirming the hypothesis as necessary to account for the experimental results.

sclerometer

Instrument used to determine the absolute hardness of a mineral. A mineral is locked into position , and a Diamond pin pushes down and slightly scratched the mineral. The amount of pressure needed for the Diamond pin to be pushed down to scratch the mineral determines its hardness.

sea arch

A landform produced by coastal erosion of a prominent headland. Sea arches form when sea caves are excavated so deeply by crashing waves that two caves eroding on opposite sides of the headland become joined. The overlying rocky roof is left as an arch.

sea cave

The notches in the sides of a prominent coastal rocky headland eroded by crahing waves.

sea-floor spreading

The formation and growth of oceans that occurs following rifting and is characterized by eruptions along mid-ocean ridges, forming new oceanic lithosphere, and expanding ocean basins. See also divergence.

seamount

A conical underwater mountain formed by a volcano and rising 1000 meters or more from the sea floor.

sea stack

A steep, isolated island of rock, separated from a headland by the action of waves, as when the overhanging section of a sea arch is eroded.

seawall

A wall of stone, concrete, or other sturdy material, built along the shoreline to prevent erosion even by the strongest and highest of waves. See also riprap.

secondary

Altered to create a new mineral.

secondary coast

A coast shaped primarily by erosion or deposition by sea currents and waves.

secondary enrichment

The process by which a metal deposit becomes concentrated when other minerals are eliminated from the deposit, as through dissolution, precipitation, or weathering.

secondary mineral

Mineral altered to a new form after undergoing a chemical change. An example is a mineral in the oxidation zone that transformed into another mineral through weathering.

sectile

Able to be cut into by a knife or other sharp object. A form of tenacity.

sediment

A collection of transported fragments or precipitated materials that accumulate, typically in loose layers, as of sand or mud.

sedimentary environment

The continental, oceanic, or coastal surroundings in which sediment accumulates.

sedimentary facies

1. A set of characteristics that distinguish a given section of sedimentary rock from nearby sections. Such characteristics include mineral content, grain size, shape, and density. 2. A section of sedimentary rock so characterized.

sedimentary rock

A rock made from the consolidation of solid fragments, as of other rocks or organic remains, or by precipitation of minerals from solution.

sedimentary structure

A physical characteristic of a detrital sediment that reflects the conditions under which the sediment was deposited.

sedimentation process

Process in which sediment transforms into sedimentary rock.

seismic gap

A locked fault segment that has not experienced seismic activity for a long time. Because stress tends to accumulate in seismic gaps, they often become the sites of major earthquakes.

seismic moment

A numerical means of measuring an earthquake's total energy release. It is calculated by measuring the total length of fault rupture and then factoring in the depth of rupture, total slip along the rupture, and the strength of the faulted rocks.

seismic profiling

The mapping of rocks lying along and beneath the ocean floor by recording the reflections and refractions of seismic waves.

seismic tomography

The process whereby a computer first synthesizes data on the velocities of seismic waves from thousands of recent earthquakes to make a series of images depicting successive planes within the Earth, and then uses these images to construct a three-dimensional representation of the Earth's interior.

seismic wave

One of a series of progressive disturbances that reverberate through the Earth to transmit the energy released from an earthquake.

seismogram

A visual record produced by a seismograph and showing the arrival times and magnitudes of various seismic waves.

seismograph

A machine for measuring the intensity of earthquakes by recording the seismic waves that they generate.

seismology

The study of earthquakes and the structure of the Earth, based on data from seismic waves.

selenides subgroup

Group of sulfides the contain one or more true metals combined with the semi-metal selenium.

selvage

The area of the point of contact between a vein and the surrounding rock.

semi-metal

Element or alloy exhibiting certain properties of the metals and certain properties of the non-metals. They are opaque with a metallic luster, and combine with other elements to form minerals as metals do. In all other aspects, they act like non-metals.

semi-metallic elements

The semi-metallic elements are minerals belonging to the native elements group and are composed of pure semi-metallic elements or semi-metallic alloys. They are opaque with a metallic luster, and combine with other elements to form minerals (i.e. Arsenides, Tellurides) the same way the metallic elements do.

semi-precious stone

Gem or gemstone used in jewelry but lacks in one or more property (such as luster, hardness, and rarity) that would make it into a precious gemstone.

series

A series is a mineral group consisting of minerals that have a nearly identical crystal structure. The only difference between the minerals in a series is the type of elements contained in the crystal structure of the mineral. This means that there must be at least two defined minerals in a series: one mineral containing one particular element, and one mineral containing a different element. These two minerals are known as the end members, or anchor members. In-between the end members minerals as a combination of both anchor members exist. Sometimes, these intermediary minerals are given names.

setting

The proper placement of a gem on an ornament, or the ordained area for the placement of a gem.

shaft

A long, narrow passage in underground mines created for the extraction of valuable material.

shale

A sedimentary rock composed of detrital sediment particles less than 0.004 millimeter in diameter. Shales tend to be red, brown, black, or gray, and usually originate in relatively still waters.

sheaflike

Synonym to wheat sheaf.

shearing stress

Stress that slices rocks into parallel blocks that slide in opposite directions along their adjacent sides. Shearing stress may be caused by transform motion.

sheet silictes

Another name for phyllosilicates. Group of silicate minerals that have each set of tetrahedrons surrounded by three oxygen atoms, forming a sheet like structure.

shelly fracture

Synonym of conchoidal fracture.

shield volcano

A low, broad, gently sloping, dome-shaped structure that forms over time as repeated eruptions eject basaltic lava through one or more vents and the lava solidifies in approximately the same volume all around.

shock metamorphism

The metamorphism that results when a meteorite strikes rocks at the Earth's surface. The meteoric impact generates tremendous pressure and extremely high temperatures that cause minerals to shatter and recrystallize, producing new minerals that cannot arise under any other circumstances.

shoreline

The boundary between a body of water and dry land.

short wave

A wavelength of ultraviolet light. Many minerals display fluorescence when exposed to shortwave ultraviolet light. Commonly abbreviated as SW.

silica

Radical of silicon and oxygen. Also term for any material composed of only silicon and oxygen (and can include water), such as Quartz, Chalcedony, and Opal.

silicafied

Having been transformed into silica. An example is petrified wood, or wood that was completely replaced by silica.

silica group

Group of silicate minerals (tectosilicates) composed only of silica (silicon dioxide -- SiO2 ). The minerals in this group are all the varieties of Quartz, Chalcedony, Opal, Tridymite, and Cristobalite (and a few rarer forms of silicon dioxide). Although Opal contains water in addition to silica, it is nevertheless in the silica group. The Silica Group is also known as the Quartz Group.

silicate

One of several rock-forming minerals that contain silicon, oxygen, and usually one or more other common elements.

silicates

Group of minerals containing various amounts of the elements silicon and oxygen.

silicon oxygen tetrahedron

A four-sided geometric form created by the tight bonding of four oxygen atoms to each other, and also to a single silicon atom that lies in the middle of the form.

silky luster

Luster of minerals that have a very fine fibrous structure, causing it to display similar optical properties to silk cloth.

sill

A concordant pluton that is substantially wider than it is thick. Sills form within a few kilometers of the Earth's surface. See also dike. A horizontal "sheet" of igneous rock interjected between rock that was there before the igneous rock. A famous example is the Palisades Sill right near on the western side of the Hudson River right near New York City.

silt

Accumulation of very small grains of rock, finer than sand.

simple oxides

Compounds of metallic elements combined with oxygen. The simple oxides are a subgroup of the oxide group.

simple sulfides

Group of sulfides that contain one or more true metals combined with sulfur.

sinkhole

A circular, often funnel-shaped depression in the ground that forms when soluble rocks dissolve.

sinter

Mineral deposit formed by mineral-rich spring water which comes to the surface and loses its capacity to withhold the dissolved mineral, thereby depositing it and forming a growing mound.

sixling

Rutile twin - Two or more crystals that twin in a repeated pattern ("repeated twinning") as depicted in the figure below. Named after the mineral Rutile, which most frequently exhibits this form of twinning. If there are six repeated crystals (i.e. another three crystals are added to the figure below in the same pattern), the agglomerate forms a circular structure, known as a sixling.

skeletal

Aggregate synonymous with dendritic. Some references note a difference in that skeletal is a single, tree-like entity, whereas dendritic is the same pattern implanted in rock.

slab

Thick slice cut out of a solid mineral; a portion of the mineral.

slag

Glassy substance formed as a by-product from the smelting of metallic ores.

slate

A fine-grained, foliated metamorphic rock that develops from shale and tends to break into thin, flat sheets.

slide

The mass movement of a single, intact mass of rock, soil, or unconsolidated material along a weak plane, such as a fault, fracture, or bedding plane. A slide may involve as little as a minor displacement of soil or as much as the displacement of an entire mountainside.

slip face

The steep leeward slope of a dune.

slip plane

A weak plane in a rock mass from which material is likely to break off in a slide.

slump

1. A downward and outward slide occurring along a concave slip plane. 2. The material that breaks off in such a slide.

smelt

To melt ores for the extraction of a valuable metal they contain.

smooth fracture

Synonym of even fracture

snowline

The lowest point at which snow remains year-round.

soil

The top layer of the earth's surface, which is composed of tiny rock particles mixed together with decaying organic matter.

soil horizon

A layer of soil that can be distinguished from the surrounding soil by such features as chemical composition, color, and texture.

soil profile

A vertical strip of soil stretching from the surface down to the bedrock and including all of the successive soil horizons.

solid solution

A series formed when there are minerals in-between two isomorphous minerals. An example is the Plagioclase Feldspar group, which contains Albite and Anorthite as the anchor minerals, and minerals varying in amounts of those two minerals. Solid solutions may also be composed of minerals with a definite structure where one element may be minutely replace by another, but is too insignificant to be mentioned in the structure of that mineral.

solidify

Transforming from a liquid state to a solid state.

solifluction

A form of creep in which soil flows downslope at a rate of 0.5 to 15 centimeters per year. Solifluction occurs in relatively cold regions when the brief warmth of summer thaws only the upper meter or two of regolith, which becomes waterlogged because the underlying ground remains frozen and therefore the water cannot drain down into it.

soluble

Able to be dissolved. Solubility is the condition of being soluble.

sorosilicates

Group of silicate minerals that are composed of groups of two tetrahedrons where one of the oxygen atoms is shared by both tetrahedrons; the other three oxygen atoms are not shared by another tetrahedron.

sorting

The process by which a given transport medium separates out certain particles, as on the basis of size, shape, or density.

source rock

A rock in which hydrocarbons originate.

spar

Any non-metallic, lightly colored mineral with good cleavage.

specific gravity

The ratio of the weight of a particular volume of a given substance to the weight of an equal volume of pure water.

specimen

A mineral or rock of interest to collectors or scientists.

spectra

Plural of spectrum.

spectral

Having to do with the spectrum

spectrograph

Device used to observe and record spectral changes.

spectrophotometer

Device used to to measure the brightness of different portions of the spectrum.

spectroscope

Device, such as a prism, which refracts white light and produces a spectrum which can be observed.

spectroscopy

The science and study of the spectrum.

spectrum

Composite of white light, which are the colors of the human eye can see. The spectrum is composed of the colors red, orange, yellow, green, blue, indigo, and violet in that order.

speleothem

A mineral deposit of calcium carbonate that precipitates from solution in a cave.

sphenoidal

Prism with wedge shaped corners, formed from a bipyramid that did not properly develop.

spheroidal weathering

The process by which chemical weathering, especially by water, decomposes the angles and edges of a rock or boulder, leaving a rounded form from which concentric layers are then stripped away as the weathering continues.

spherulitic

Aggregate consisting of rounded, ball like structures composed of radiating crystals. Spherulite is term ussed to describe any  mineral composed of spherulitic aggregates.

spinel twin

Form of contact twinning, in which two octahedral crystals that twin at the base, as depicted in the figure below. Named after the mineral Spinel, which most frequently exhibits this form of twinning.

spit

A narrow, fingerlike ridge of sand that extends from land into open water.

splendent luster

Synonym of metallic luster.

splintery habit

Crystal habit where crystals are long, thin, straight splinters. "Splintery" also describes an aggregate composed of such crystals.

splintery fracture

Fracture forming elongated splinters. All fibrous minerals fall into this category.

stable

Able to withstand normal environments without disintegrating.

stalactite

An icicle-like mineral formation that hangs from the ceiling of a cave and is usually made up of travertine, which precipitates as water rich in dissolved limestone drips down from the cave's ceiling. See also stalagmite.

stalactitic

Aggregate composed of long, icicle-like formations, like stalactites.

stalagmite

A cone-shaped mineral deposit that forms on the floor of a cave and is usually made up of travertine, which precipitates as water rich in dissolved limestone drips down from the cave's ceiling. See also stalactite.

stalagmitic

Shaped as a stalagmite, as a tall-domed structure. Many times confused with the term stalactitic, and many times substituted for that word.

star dune

A dune with three or four arms radiating from its usually higher center so that it resembles a star in shape. Star dunes form when winds blow from three or four directions, or when the wind direction shifts frequently.

staurolite twin

Form of penetration twinning where two monoclinic crystals form interpenetrating twins at 90º, forming a cross, as depicted in the figure below. Named after the mineral Staurolite, which most frequently exhibits this form of twinning. (Staurolite crystals may also twin at angles other than 90º, such as 60º.)

stellate

Synonym of radiating.

stock

Body of exposed igneous rock that intruded a layer of underground sedimentary rock, and is smaller than around 40 square miles (around 100 square kilometers).

stone

Small piece of rock; may or may not refer to ornamental material.

strain

The change in the shape or volume of a rock that results from stress.

stratification

The behavior of having mineral sediments embedded in sedimentary rock.

stratovolcano

A cone-shaped volcano built from alternating layers of pyroclastics and viscous andesitic lava. Stratovolcanos tend to be very large and steep.

stratum

Layer of sedimentary rock compromised of one rock type. Layers of strata containing different rocks may form parallel bands of different rock. Strata  is the plural form of stratum.

streak

The color of a mineral in its powdered form. This color is usually determined by rubbing the mineral against an unglazed porcelain slab and observing the mark made by it on the slab.

streak plate

Unglazed piece of porcelain, such as a tile, used to test a mineral's streak

stream

A body of water found on the Earth's surface and confined to a narrow topographic depression, down which it flows and transports rock particles, sediment, and dissolved particles. Rivers, creeks, brooks, and runs are all streams.

stream discharge

The volume of water to pass a given point on a stream bank per unit of time, usually expressed in cubic meters of water per second.

stream terrace

A level plain lying above and running parallel to a stream bed. A stream terrace is formed when a stream's bed erodes to a substantially lower level, leaving its floodplain high above it.

stress

The force acting on a rock or another solid to deform it, measured in kilograms per square centimeter or pounds per square inch.

striated

Exhibiting tiny parallel lines or grooves.

striation

1.) One of a group of usually parallel scratches engraved in bedrock by a glacier or other geological agent.
2.) Tiny, parallel lines seen on some crystal faces.

strike

1. ) The horizontal line marking the intersection between the inclined plane of a solid geological structure and the Earth's surface.
2. The compass direction of this line, measured in degrees from true north.

strike-slip fault

A fault in which two sections of rock have moved horizontally in opposite directions, parallel to the line of the fracture that divided them. Strike-slip faults are caused by shearing stress.

structural geology

The scientific study of the geological processes that deform the Earth's crust and create mountains.

structure

1.) The form of a mineral based on the way its molecules are arranged.
2.) Features exhibited in rock portions, for example flow banding and bedding.

stubby

Short and fat. Used in describing crystals.

stud

Small jewel placed on an ornament, such as an earring. May also refer to the verb form of setting with a stud. Sometimes additionally refers to a cable that holds together a metallic ornamental chain, such as a necklace.

subconchoidal fracture

Mineral fracture that falls somewhere between conchoidal and even; being smooth with irregularly rounded corners.

subduction

The sinking of an oceanic plate edge as a result of convergence with a plate of lesser density. Subduction often causes earthquakes and creates volcano chains.

subgroup

The next level of mineral classification after categorization in groups.

sublimate

To go from a solid state directly to a gaseous state without becoming liquid.

sub metallic luster

Luster of opaque to nearly opaque minerals with very good reflective properties.

subsidence

The lowering of the Earth's surface, caused by such factors as compaction, a decrease in groundwater, or the pumping of oil.

sulfates

Group of minerals that contains one or more metallic element in addition to the sulfate radical (SO₄). All sulfates are transparent to translucent and soft. Most are heavy and lightly colored, and some are soluble in water. Rarer sulfates exist containing substitutions for the sulfate radical, such as the chromates, where it is replaced by a chromate radical (CrO₄). The sulfates can be divided into the Hydrous sulfates and the Anhydrous sulfates. The chromates are usually classified as a sub-group of the sulfates.

sulfides

Group of minerals that are compounds of one or more metallic elements combined with the non-metallic element sulfur. The sulfur acts as a semi-metal when it combines to form a sulfide mineral. In some sulfides, the semi-metals arsenic, antimony, selenium, and tellurium substitute for the sulfur. There are different types of sulfides known as: Simple sulfides, Arsenides, Antimonides, Tellurides, Selenides, and  Sulfosalts.

sulfosalts

Group of sulfides that contain one or more true metals, sulfur, and either the semi-metals antimony, arsenic, or bismuth. They are generally soft, have a metallic luster, and are heavy and uncommon.

sulfuric acid

Chemically H₂SO₄, it is a corrosive, oily, acid used for manufacturing chemicals, medicine, paints, detergents, and explosives. It is a very destructive liquid and will destroy many minerals.

surface wave

One of a series of seismic waves that transmits energy from an earthquake's epicenter along the Earth's surface. See also body wave.

surge

To flow more rapidly than usually. Said of a glacier.

surrounding rock

The rock surrounding a vein or embedded crystal.

suspended load

A body of fine, solid particles, typically of sand, clay, and silt, that travels with stream water without coming in contact with the stream bed.

suture zone

The area where two continental plates have joined together through continental collision. Suture zones are marked by extremely high mountain ranges, such as the Himalayas and the Alps.

swallowtail twin

Form of penetration twinning in which two monoclinic crystals twin to form a v-shaped model, as depicted in the figure below. This form of twinning is most frequently seen on the mineral Gypsum.

S wave (abbreviation for secondary wave)

A body wave that causes the rocks along which it passes to move up and down perpendicular to the direction of its own movement. See also P wave.

S-wave shadow zone

The region within an arc of 154° directly opposite an earthquake's epicenter that is marked by the absence of S waves. The S-wave shadow zone is due to the fact that S waves cannot penetrate the liquid outer core. See also P-wave shadow zone.

syenite

Igneous rock containing alkali feldspars. Contains mica and pyroxene minerals.

symmetry

Exact proportion from an intermediate center horizontal line, vertical line, or central point. If an object has symmetry, than it can be rotated or flipped and appear the the exact same way it was before the rotate or flip. The axes (x axis and y axis) are imaginary lines drawn through the center of the shape; the x axis going in a horizontal direction, the y axis going in a vertical direction. There are three types of symmetry:
a) Symmetry about a center point:  Will retain the same shape even if flipped over both the x and y axes. Can be rotated 90° and will still retain the same shape.
b) Symmetry about the x axis: Will retain the same shape if flipped over the the x axis.
c) Symmetry about the y axis:  Will retain the same shape if flipped over the the y axis.

syncline

A concave fold, the central part of which contains the youngest section of rock. See also anticline.

synthetic  

Man made. Synthetic gems are created using molten chemicals to solidify and form the gem.