Welcome to the Mineral and precious stone glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z  All terms

S

Saccharoidal

Composed of tiny, equidimensional 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) 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.

Scalenohedral

Shaped as a scalenohedron.

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.
A mixture of a rhombohedron and scalenohedron also exists. It is sometimes called a rhomb-scalenohedron.

Scales

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

Scaly

Describing an aggregate of scales.

Scepter

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

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. (See Hardness in mineral properties for more information.)

Schiller

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

Schist

Type of metamorphic rock made up of parallel layers of flaky, micaceous minerals.

Secondary

Altered to create a new mineral. (See "secondary mineral")

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.

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

Sediment

Eroded pieces of rock that get carried away in streams and form deposits in them, which eventually cement together and form sedimentary rock.

Sedimentary rock

Rock formed by the weathering of substances; forming layers from accumulation of minerals and organic substances.

Sedimentation process

Process in which sediment transforms into sedimentary 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

Having the attributes of a semi-metal.

Semi-metallic elements (subgroup)

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

It is very hard to define a mineral series in writing. The following is a bit confusing but is the simplest way to put it in words.

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. An example of this is a mineral series known as the Olivine group. In the Olivine group, the two end members are Forsterite and Fayalite. Forsterite and Fayalite have a crystal structure that is identical, except that Forsterite is composed of magnesium (Mg), and Fayalite is composed of iron (Fe).

Forsterite	Mg2SiO4
Fayalite	Fe2SiO4

Another member of the Olivine group is Chrysolite. Chrysolite is an intermediary member, so it has a varying amount of magnesium and iron.

Chrysolite

(Mg,Fe)2SiO4

The amount of magnesium to iron in Chrysolite is not defined, and can range from 1:99 to 99:1. However, in certain mineral series, intermediary members are given names based on defined percentages of the elements they contain. For example, if an intermediary member contained 20% Mg and 80% Fe, it might be classified as a different mineral than 80% Mg and 20% Fe.

 

Some mineral series, such as the Spinel series, contain more than two end members. This means there can be many different combinations of intermediary members.

Spinel Series (anchor members)
Common Spinel	MgAl2O
Gahnite	ZnAl2O
Hercynite	FeAl2O
Galaxite	MnAl2O

Some possible combinations might be:

(Mg,Zn)Al2O

(Mg,Fe)Al2O

(Zn,Fe)Al2O

(Mg,Zn,Fe)Al2O

(Mg,Fe,Mn)Al2O

Most of these possible combinations do not have names, but a few, such as Gahnospinel,(Mg,Zn)Al₂O₄, do.

 

In a few complex mineral series, such as Garnet, more than one element may be replaced by another.

Garnet member
Pyrope	Mg3Al2Si3O12
Almandine	Fe2+3Al2Si3O12
Spessartine	Mn3Al2Si3O12
Grossular	Ca3Al2Si3O12
Andradite	Ca3Fe3+2Si3O12
Uvarovite	Ca3Cr2Si3O12

The mineral Pyrope and the mineral Uvarovite contain TWO elements that are different, and yet they are still in the same series, since they are identical in crystal structure, and can (theoretically) form intermediary members.
In large series such as Garnet, nearly hundreds of possible intermediary combinations can exist. However, this number is greatly restricted since the laws of chemistry only allow certain members to combine with others.

A mineral series may contain a member with the same name. For example, the Skutterudite series contains three minerals, and the name of one of them is Skutterudite.

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.

Shortwave

A wavelength of ultraviolet light. Many minerals display fluorescence when exposed to shortwave ultraviolet light.

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 gel

Chemical that absorbs moisture from air.

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. See Polymorphs of SiO2 for more detailed information on the minerals in the silica group.

Silicates (group)

Group of minerals containing various amounts of the elements silicon and oxygen. For more information, see "All About the Silicates Group".

Sill

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.

Silky (luster)

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

Silt

Accumulation of very small grains of rock, finer than sand

Simple oxides (subgroup)

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

Simple sulfides (subgroup)

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

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.

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.

Smelt

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

Soil

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

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.

Solubility

The condition of being soluble.

Soluble

Able to be dissolved.

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

Spar

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

Specific gravity

The weight ratio of a mineral due to the density of the atomical arrangement and the heaviness of the elements it contains. (See Specific Gravity in mineral properties for more information.)

Specimen

A mineral or rock of interest to collectors or scientists.

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.

Sphenoidal

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

Spherulite

Any mineral composed of spherulitic aggregates.

Spherulitic

Aggregate consisting of rounded, ball like structures composed of radiating crystals. A famous example is Wavellite.

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.

Splintery

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, unlike unstable minerals.

Stalactites

Icicle-like formations on the roof of caverns created when mineral-rich water drips down from the roof and the dissolved mineral accumulates into the icicle-like formation. May be confused with stalagmites, which are tall-domed formations on the bottom of caverns built up from the mineral-rich water depositing the dissolved mineral on the floor.

Stalactitic

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

Stalagmites

Tall-domed formations on the bottom of caverns built up from mineral-rich water that deposits the dissolved mineral on the floor, growing upwards. May be confused with stalactites, which are icicle-like formations on the ceiling of caverns created from the mineral-rich water dripping down, and the dissolved mineral accumulates into the formation.

Stalagmitic

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

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.)

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.

Streak

The color of the powder of a mineral. Streak can be tested by rubbing a mineral against a hard, white, porcelain object (streak plate), and the "streak" that remains on the swiped area is the color of the streak of the mineral. (See Streak in mineral properties for more information.)

Streak plate

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

Striated

Exhibiting tiny parallel lines (or grooves -- depending if it sounds better that the cup is half empty rather than half full) on crystal faces.

Striations

Tiny, parallel lines seen on some crystal faces.

Stratification

The behavior of having mineral sediments embedded in sedimentary rock.

Stratum

Layer of sedimentary rock compromised of one rock type. Layers of strata containing different rocks may form parallel bands of different rock.

Structural

Relating to the structure of a mineral.

Structure (minerals)

The form of a mineral based on the way its molecules are arranged. Also short for Chemical structure.

Structure (rocks)

Features exhibited in rock portions, for example flow banding and bedding.

Stubby

Short and fat. Stubby crystals are short and fat.

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.

Subgroup

The next level of mineral classification after categorization in groups (definition 3).

Sublimate

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

Sublimation

The act of sublimating.

Submetallic (luster)

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

Sulfides (group)

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.

Sulfosalts (subgroup)

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

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

Surrounding rock

The rock surrounding a vein or embedded crystal.

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.

Syenite

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

Symmetrical

Containing perfect symmetry.

Symmetry

Synthetic gem

Gem created by man using molten chemicals to solidify and form the gem.