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The Salina Beds belong to the Upper Silurian of North America, and are the lower subdivision of the Onondaga group. They consist mainly of red marls with limestone, dolomite, and extensive beds of rock-salt, especially in the state of New York. As a whole, these rocks are unfossiliferous, and seem to have been laid down in shallow waters exposed to desiccation. They extend northwards into Ontario, crossing the Niagra river a little above Niagra Falls.
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Sand is small particles (between 0.0625 and 2 mm in diameter) of mineral matter, usually quartz. The purest quartz sands are white in colour and used for making glass. Other sands may be various colours dependant upon the minerals they contain.
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Sandstone is a common sedimentary rock made up of tiny grains of quartz held together by a type of cement. Sandstone is produced by sand which has been deposited and cement precipitated between the grains by groundwater percolating through it. The most common cements are calcium carbonate, silica and iron oxide. Sandstone is an important building material in the USA where many of the brownstone houses in the north-east cities are made of sandstone.
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Sanidine is a clear, glassy, often cracked variety of orthoclase feldspar, which is confined to modern volcanic rocks, such as trachyte, rhyolite and phonolite. It is found in the Rhine, Italy and Hungary.
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Sapphire is a coloured form of corundum, often blue and transparent. The colouration is caused by the presence of iron oxide and titanium oxide. Artificial sapphires are made by melting powdered corundum at high temperature with iron and titanium.
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Sard is a brownish red variety of Chalcedony.
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Sassolite (Boric Acid) is a vitreous, white mineral found in volcanic areas and in hot springs. It is named after Sasso in Italy where it was first discovered.
Sassolite has the formulae H3BO3 and a relative hardness of 1.
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Saussurite is a waxy-looking, white or pale green substance which results from the alteration of feldspar in rocks such as gabbro. It is a very fine admixture of garnet, zoisite, albite and other minerals.
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Scapolite has the formulae (Na,Ca,K)4A13(Al,Si)3Si6O24(Cl,SO4,CO3) and a relative hardness of 6. It shows fluorescence. Occurs in the crystalline schists, gneisses, and often is probably derived from the alteration of plagioclase feldspars. Also occurs in crystalline limestones formed by metamorphic contact or igneous intrusion. Associated with diopside, amphibole, garnet, apatite, and zircon.
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Scheelite is a mineral occurring in hydrothermal veins and in placer deposits, in contact metamorphic rocks and in pegmatite. It an important ore of tungsten.
Scheelite was confirmed as a distinct species of mineral in 1821 and named in honour of the Swedish chemist Carl Scheele. Scheelite is associated with cassiterite, topaz, fluorite, apatite, molybdenite, and wolframite. Sometimes
scheelite is found with gold. It has the formulae CaWO4 and a relative hardness of 5.
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Schist is a medium to coarse-grained metamorphic rock formed mainly from finely layered sheets of platy or elongated minerals such as mica. These sheets are interleaved with feldspar and quartz.
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Schorl is a rock comprised of quartz and black tourmaline (schorl). It is of igneous origin and occurs associated with granite and crystalline schists. It has a granular texture and is usually a grey colour. It is a frequent associate of tin-bearing veins in all parts of the world.
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Schwazite is a variety of Tetrahedrite containing up to 17 percent mercury.
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Scolecite is a mineral found in lavas and contact metamorphic deposits. It is a hydrated silicate of calcium and aluminium and has the formulae Ca(Al2Si3)O103H2O and a relative hardness of 6. Scolecite was confirmed as a distinct species of mineral in 1813.
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A scoria is a cavity in igneous rock, caused by an escape of gas or steam. When such a cavity contains a mineral it is known as a amygdule.
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Scorodite is a mineral of the varicite group occurring in the oxidized portions of metallic veins as an alteration of arsenic containing minerals. It has the formulae FeAsO42H2O and a relative hardness of 4. Scorodite was confirmed as a distinct species of mineral in 1818.
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Secondary minerals refers to minerals formed by the alteration of pre-existing minerals.
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Sedimentary rock is a deposit that has been laid down by water, wind, ice, or gravity. The material of which sedimentary rocks are composed has usually been transported from its source. They have accumulated at or near the Earth' s surface at normal temperatures and pressures, and are thus distinguished from igneous rocks, which have originated as magma in a molten or semi- molten state, and from metamorphic rocks, which have been produced by the effects of heat or pressure. Many sedimentary rocks were deposited in water in which the transported material was in a state of suspension or solution. After deposition they have been consolidated. Some, such as loess, were deposited by the wind; some, such as boulder clay, are the result of glacial action; some have simply accumulated in place. Sediments can be divided into three groups: clastic rocks, chemical precipitates, and organic sediments. Of these, clastic sediments are the most abundant. They are made up of fragments of pre-existing rocks. Clays, sands, and gravels are in this category.
Chemical precipitates include some limestones (the English Chalk, for example) and deposits formed by the evaporation of lakes or seawater. These deposited rocks include gypsum and halite. Organic sediments are those formed largely of the remains of once-living organisms: examples are coal, oil shale, and limestones made mainly of fossil material.
By volume, sedimentary rocks make up only five per cent of the known crust of the Earth, compared with 95 per cent of igneous rocks. They are, however, exposed on over two-thirds of the Earth's land surface, forming thin but extensive deposits. The commonest types are shales, sand-stones, and limestones. The earliest known sedimentary rocks came from the Barberton Mountain Land of South Africa; these have been dated as 3,500 million years old.
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Selenite is a clear, transparent variety of gypsum often found in large twinned crystals shaped like arrow-heads or rhombus. The crystals have a perfect cleavage like mica, but are less flexible and somewhat softer. Selenite has a relative hardness of 2 and the formulae CaSo42H2O.
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Serpentine is a common mineral group with a relative hardness of 4. It is usually an alteration product of some magnesium silicate, especially olivine, pyroxene, and amphibole. It is frequently associated with magnesite, chromite, and magnetite. It has the formulae Mg6(Si4O10)(OH)8.
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Shale is a fine black sedimentary rock that splits easily into thin plates along well-defined planes parallel to the original stratification. Shale is composed of a complex mixture of microscopic clay minerals plus mica and quartz. Shale is often rich in fossils and dinosaur tracks. Shale is formed in quiet water environments, such as lake bottoms, river floodplains, tidal flats, marshes and the floors of deep oceans, where the finest particles carried by the water have settled. These clays gradually petrify forming shale.
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Siderite is native iron carbonate, an ore of iron that becomes magnetic when heated. It is frequently found as an impure admixture with clay materials and also in concretions with concentric layers. It has a relative hardness of 5.
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Silica refers to silicon dioxide (SiO2). A very common mineral that is found in many forms including quartz, opal, chert.
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Silicates refers to a group of minerals composed chiefly of SiO4. Ex: quartz, orthoclase.
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Silky refers to a silk-like lustre on a mineral. Results from a fine, fibrous and parallel surface.
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Sill is a geological term for a sheet of igneous rock intruded into overlaying beds and lying nearly horizontal over a large area.
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Sillimanite (fibrolite or bucholzite) is a fibrous silicate, somewhat rare mineral found as a constituent of gneiss and schist in metamorphic rocks, and often occurs with corundum. It has the formulae Al2SiO5 and a relative hardness of 7. Sillimanite was first confirmed as a distinct species of mineral in 1824 and was named in honour of Benjamin Silliman, professor of chemistry at Yale University. Industrially, sillimanite is used in spark-plugs for automobiles.
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Silt is a class of rock between 0.004 and 0.0625 mm in diameter.
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The Silurian was the fifth geological period, 335,000,000 years ago. This period marked the appearance of the first land plants.
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Silver is a white, ductile metallic element that is sonorous, very malleable, capable of a high degree of polish, and chiefly univalent with it's compounds and has the highest thermal and electrical conductivity of any substance. It has the symbol Ag.
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Skarn is a calcite rock formed from pre-existent limestone and dolostone when molten magma escapes from the Earth's mantle and becomes injected into the upper crust where it forms igneous intrusions altering the existing rocks by its heat.
Skarn is often rich in minerals.
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Skutterudite is an important ore of cobalt and nickel usually formed in hydrothermal veins. It is associated with native silver, bismuth, calcite and arsenopyrite. Skutterudite is an arsenide of cobalt, iron and nickel and has a relative hardness of 6. Skutterudite was confirmed as a distinct species of mineral in 1845.
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Slate is a greyish metamorphic rock. Slate is commonly found where shale has been subjected to low-grade regional metamorphism of low pressure and very little heat during episodes of mountain building. It is very fine grained and splits well into thin sheets. It is composed of mica, quartz and other minerals and is used for roofing tiles and sheets.
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In geology, slickensides are the wall-faces or polished surfaces found along the joints and fault planes of rocks. They are usually marked with fine striations of the sides of the fissure over one another.
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Slime is the name applied to that portion of crushed ore which, owing to its impalpable and minutely divided state and the presence of colloidal substances, settles very slowly from water, forming an impervious mass.
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Smithsonite is a secondary mineral formed in parts of zinc and copper deposits that have been oxidised by the action of air and water. It is one of the calamines and was confirmed as a distinct species of mineral in 1832 and named after James Macie Smithson the British chemist and mineralogist. Smithsonite is grey, white, light green or brown in colour with a glassy lustre. It has the formulae ZnCO3 and a relative hardness of 6. It is an ore of zinc usually found with zinc deposits in limestone beds.
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Snake stone (also known as Water of Ayr Stone or Scotch Stone) is a variety of whetstone. It is a light grey carboniferous shale, used for polishing marble and copper plates as well as sharpening tools. Snake stone is found at Bridge of Stair on the Ayr in Scotland.
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Soapstone is a popular name for steatite.
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Sodalite is a usually attractive blue colour mineral found in limestones and used for polished slabs and for carved ornaments. It is a chlorosilicate of sodium and aluminium with the formulae Na4Al3(SiO4)3Cl and a relative hardness of 6. Sodalite was confirmed as a distinct species of mineral in 1811 and gets its name from its chief metal - sodium.
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Soil creep is the name given to slow movements of the particles of soil along sloping surfaces. Gradual loosening of upper layers of soil is caused by the action of frost, rain and the weather in general, which assisted by gravity aids in bringing loosened material from higher to lower levels. Soil creep in the Culebra cut interfered with the continuous use of the Panama Canal when it was first built.
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In geology, Solenhofen Stone is a name given to a fine-grained smooth-textured limestone, derived mainly from Solenhofen in Bavaria. The stone is found in beds of 15 meters or more thick, and is a deposit of the Upper Jurassic, and is particularly rich in fossils, notably those of pterodactyls and the archaeopteryx. Solenhofen Stone was widely used in lithography.
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Sorbite is a compound of iron and carbon intermediate between austenite and pearlite, virtually an extremely minute form of the latter. Sorbite is named after the English geologist Henry Sorby.
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Specific gravity refers to the relative density of a mineral. It is the ratio of:; Weight in Air/ (Weight in Air - Weight in Water). ;This measurement is an easily accomplished procedure using a simple balance or spring scale.
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Sperrylite is a rare natural compound of platinum and arsenic found in the nickel mines of Sudbury in Canada. It has the formulae PtAs2 and a relative hardness of 7.
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Spessarite is a variety of garnet of a dark red colour found in the Ural Mountains and in Virginia, USA.
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Sphalerite or blende, is the main ore of zinc. Sphalerite is associated with galena, pyrite, marcasite, chalcopyrite, calcite. Sphalerite is formed mainly in hydrothermal veins and as a replacement deposit in limestones and in veins in igneous rocks. It has the formulae (Zn,Fe)S and a relative hardness of 4.
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Sphene (titanite, calcium silicate or titanate) is a variety of titanite and a source of titanium. A rather common accessory mineral in igneous rocks, it is a light yellow or green colour and sometimes a dark brownish green colour. It is often found as crystals, particularly in the Tirol, and is commonly associated with chlorite. It has the formulae CaTiO(SiO4) and a relative hardness of 6.
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Spinel is a common metamorphic mineral occurring imbedded in crystalline limestone, gneisses, and serpentine. Spinel occurs as a common accessory mineral in many dark igneous rocks. When transparent and finely coloured it is often confused for ruby and is used as a gem stone. An oxide of magnesium and aluminium it has the formulae MgAl2O4 and a relative hardness of 8.
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Spodumene is a mineral confirmed as a distinct species in 1800 it is the main source of the metal lithium. Spodumene is found occasionally as very large crystals in pegmatic dikes. A silicate of lithium and aluminium, it has the formulae LiAlSi2O6 and a relative hardness of 7.
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In geography, a stack describes an isolated column close to the sea shore. In the erosion of cliff faces fragments are left separated from the rock face, and may be honeycombed with caves, and will ultimately disappear. The Needles off the west extremity of the Isle of Wight are a conspicuous example of stacks.
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A stalactite is a mass of calcareous matter hanging in caves, formed by the filtration of water containing calcium bicarbonate in solution through holes or pores in the cave roof. the evaporation of the water and carbonic acid gas leaves behind it a deposit of limestone which continues to increase in size so long as the water drops.
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A stalagmite is a column of calcium carbonate rising from the floor of a cave, formed by water containing the mineral falling from the roof or from a stalactite.
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Stannite or tin pyrites is a sulphostannate of copper and iron found in tin deposits in Cornwall.
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Staurolite is an brown, vitreous accessory mineral found in crystalline schists, slates, and sometimes gneisses and often associated with garnet, kyanite, and tourmaline. It has the formulae (Fe,Mg,Zn)2Al9Si4O23(OH) and a relative hardness of 8.
Staurolite was confirmed as a distinct species of mineral in 1792 and often forms in distinctive cruciform shapes from which it is named.
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Steatite (soapstone) is a variety of talc, hydrated magnesic silicate, usually devoid of a distinct crystalline structure. It is white, blue-grey, green or brown in colour, soft and easy to cut and heat-resisting. Since the earliest of times steatite has been used for ornaments and carvings. In a powdered form it is an ingredient in soaps, paints, lubricants and French chalk.
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Stellerite is a mineral of the zeolite group closely resembling stilbite.
Stellerite was confirmed as a distinct species of mineral in 1909 after years of being confused with stilbite, and was named after Georg Steller the German explorer and naturalist.
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Stephanite is a minor ore of silver. One of the last minerals to form in silver veins. It has the formulae Ag5SbS4 and a relative hardness of 3.
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Stibiconite is a secondary mineral formed through the oxidation of stibnite. It commonly occurs with stibnite and is sometimes pseudomorphous with it.
Stibiconite has unusual properties, it can split light passing through it into two rays and its crystals look the same from any angle. Stibiconite was confirmed as a distinct species of mineral in 1832 and is a hydrous oxide of antimony and is sometimes mined as an ore of antimony. Stibiconite has a relative hardness of between 3 and 7 depending upon whether it is scraped along the grain or against it.
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Stibnite (also known as antimonite, antimony glance and black antimony) is the major ore of antimony. It is Deposited by alkaline waters, usually in association with quartz. Stibnite is found in quartz veins or beds in granite and gneiss and may occur as a replacement in limestones and shales.
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Stilbite is a secondary mineral formed by the action of hydrothermals on pre-existent minerals. It is found in cavities in basalts and related rocks in Scotland, Ireland and the Faroe Islands. It has a relative hardness of 4. Stilbite is a member of the zeolite group and was confirmed as a distinct species of mineral in 1797. Stilbite is a hydrated silicate of sodium, calcium and aluminium and is white to red in colour and exhibits a glassy or pearly lustre.
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Stilpnomelane is a mineral forming dark coatings in schist and may also be found in iron ore deposits, commonly associated with epidote and mica. Stilpnomelane was confirmed as a distinct species of mineral in 1827 but since then debate has raged as to whether it is a simple mineral or a mixture of closely related species. Stilpnomelane is a hydrous silicate of potassium, ferrous and ferric iron, magnesium and aluminium and has a relative hardness of 3 to 4. Pure
stilpnomelane contains more ferric iron than ferrous iron, specimens containing more ferrous iron then ferric iron are sometimes known as chalcodite or ferrostilnomelane.
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Stonebrash is a soil made of small stones or broken rock. The term originated for the subsoil of north-western Wiltshire which consisted of a reddish calcaerous loam mingled with flat stones.
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Stonesfield Slate is a limestone of the Jurassic period. Stonesfield Slate is not a slate, but is so called from being thin bedded, and can be used as a replacement for slate in many instances.
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In geology, stratification refers to the natural formation of layers or 'beds' of rock by the deposit of sediment. Many stratified rocks were formed by sediment washed down rivers into the sea where they formed a deposit on the sea bed and were subsequently covered by other deposits and compressed into rock. A common example being sandstone.
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Stratum is a geological term describing a mass of sedimentary rock (a strata) of great horizontal extent, which was deposited more or less continuously on the bottom of former seas or lakes, or sometimes on the surface of flat plains or deserts. Stratified rocks are mostly sandstones, shales and limestone.
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Streak refers to the colour of the powder produced when a mineral is rubbed over the surface of a piece of unglazed, white porcelain.
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Striations refers to very small parallel grooves or narrow channels of the faces of a crystal.
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Strontianite is a natural source of strontium, named after Strontian in Argyleshire where it was discivered in 1792 by Hope. Physically it is similar to cerussite and witherite. It is associated with barite, celestite, and calcite in veins in limestone. Occasionally it is found in igneous rocks and as a gangue mineral in sulphide veins. It has the formulae SrCO3 and a relative hardness of 4.
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Strunzite is a mineral confirmed as a distinct species in 1957, and previously thought to be laurite. Strunzite has the same chemical makeup of laurite and pseudolaurite but has a monoclinic crystal system. Strunzite is a hydrated phosphate of manganese and ferric iron and appears as coatings and tufts on the surface of granite pegmatite where it formed through the alteration of primary triphylite.
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Sulphates refers to a group of minerals in which sulphate SO4 is an important part.
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Sulphides refers to a mineral group where sulphur is combined with one or more metals. The sulphides form an important class of minerals that includes the majority of the ore minerals. With them are classed the similar but rarer sulpharsenides, arsenides, and tellurides. Most of the sulphide minerals are opaque with distinctive colours and characteristically coloured streaks. Those that are non-opaque, such as cinnabar, realgar, and orpiment, have high refractive indices and transmit light only on thin edges.
The general formula for the sulphides is given as XmZn, in which X represents the metallic elements and Z the non-metallic element. The general order of listing of the various minerals is in a decreasing ratio of X:Z. The sulphides can be divided into small groups of similar structures but it is difficult to make broad generalizations about their structure. Regular octahedral or tetrahedral coordination about sulphur is found in many simple sulphides such as in galena, PbS, (with an NaCI type structure), and in sphalerite, Zns. In more complex sulphides, as well as sulphosalts, distorted coordination polyhedra may be found. Many of the sulphides have ionic and covalent bonding, whereas others, displaying most of the properties of metals, have metallic bonding characteristics.
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Sulphur (brimstone) is a non-metallic element that occurs either free or in combination with sulphates and sulphides, is a constituent of proteins, exists in several allotropic forms including yellow orthorhombic crystals, resembles oxygen chemically but is less active and more acidic, and is used especially in the chemical and paper industries, in rubber vulcanisation, and in medicine for the treating of skin diseases. It has the symbol S.
Sulphur has been known since ancient times, but was only discovered to be an element in 1809.
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Sunstone is a form of translucent feldspar found in Siberia, Norway and North America, emitting a brilliant red metallic glitter from the background like hidden fire. Sunstone is a semi-precious gemstone and is usually cut with a flat or slightly convex surface.
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Syenite is a plutonic igneous rock consisting essentially of alkali-feldspar and one or more ferro-magnesian minerals, such as augite, hornblende, or mica.
Syenite is often mistake for granite because of its colour, but has a lower silica content.
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Sylvanite is a rare ore of gold, silver, and tellurium of a steel grey, silver white, or brass yellow colour, formed in low temperature hydrothermal veins. It often occurs in implanted crystals resembling written characters, and hence is called graphic tellurium. It is associated with calaverite and other tellurides - usually in quartz gangue. It has a relative hardness of 2.
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Sylvite (sylvine) is an industrial mineral, the naturally occurring potassium chloride, and as such the main mineral ore of potassium. Sylvite has a relative hardness of two and is used as a fertilizer. Sylvite is an evaporate mineral found in sedimentary evaporate deposits such as dried-out salt lakes and seas in deserts, and is associated with halite. Sylvite was confirmed as a distinct species of mineral in 1832 but was known at least during the 17th century.
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In geology, a syncline is the dipping of the strata inwards towards the axis of an earth fold, producing a trough-shaped or basin-like arrangement of the strata. Synclines form the troughs and anticlines the arches of a series of earth folds.
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Abbreviations
Rocks & Minerals
