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Minerals

Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten. Well-formed crystals are sought by collectors and are occasionally fastened into gemstones when suitably free of flaws. Scheelite has been syn...

The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a par...

Scoria is a term used by geologists to describe an igneous rock containing many gas bubbles, or vesicules. Scoria forms when magma rich in dissolved gases is vented. As the magma encounters lower pressures, the gasses are able to escape and form bub...

Selenite (chemical formula: CaSO4·2H2O) is a hydrous calcium sulfate, meaning it is composed of oxygen, sulfur, hydrogen, calcium and water. It is basically a glassy, well-crystallized form of gypsum and is often referred to as satin spar. Seleni...

Serpentine is a group of common rock-forming hydrous magnesium iron phyllosilicate ((Mg,Fe)3Si2O5(OH)4) minerals. In mineralogy, serpentine may refer to any of 20 minerals belonging to the serpentine group. Owing to admixture, these minerals are not al...

Shale is a fine-grained sedimentary rock whose original constituents were clays or muds. It is characterized by thin laminae breaking with an irregular curving fracture, often splintery, and parallel to the often indistinguishable bedding planes. Non-f...

Siderite is a mineral composed of iron carbonate FeCO3. It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus. Both magnesium and manganese commonly substitute for the iron. Its crystals belong to the hexagonal sys...

Sillimanite is an alumino-sillicate mineral with the chemical formula Al2SiO5. Sillimanite is named after the American chemist B. Silliman (1779-1824). Occurrence Sillimanite is one of three alumino-sillicate polymorphs, the other two being andal...

Siltstone is a sedimentary rock that is intermediate in grain size between the coarser sandstone and the finer shale. As its name implies, it is primarily composed of silt, defined as grains smaller than 62 micrometres. Siltstones were at one time ofte...

Silver is a chemical element in the periodic table that has the symbol Ag (from the traditional abbreviation from the Latin Argentum) and atomic number 47. A soft white lustrous transition metal, silver has the highest electrical and thermal conductivi...

Slate is a fine-grained, homogeneous, sedimentary rock composed of clay or volcanic ash which has been metamorphosed (foliated) in layers (bedded deposits). Slate can be made into roofing shingles ('roofing slates' in the United Kingdom), because it ha...

Smithsonite, or zinc spar, is zinc carbonate ZnCO3, a mineral ore of zinc. Historically, smithsonite was identified with hemimorphite before it was realised that they were two distinct minerals. The two minerals are very similar in appearance and the t...

Sphalerite (ZnS) is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron as (Zn,Fe)S. It is usually found in association with galena, pyrite, and other sulfides along ...

Stibnite, sometimes also called antimonite, is a sulfide mineral. It crystallizes in the orthorhombic system, has hardness 2 and a grey colour. Its chemical composition is described by the formula Sb2S3 Stibnite is the most important source for the ...

Sulfur (or Sulphur; see spelling below) is the chemical element in the periodic table that has the symbol S and atomic number 16. It is an abundant, tasteless, odorless, multivalent non-metal. Sulfur, in its native form, is a yellow crystaline solid. I...

Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts. The feldspars are alkaline in character and the dark mineral is usually hornblende. ...

Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg3(SiO3)4 or Mg3Si4O10(OH)2. It occurs as foliated to fibrous masses, its monoclinic crystals being so rare as to be almost unknown. It has a perfect basal cleavage,...

Tennantite is a copper arsenic sulfide mineral. Its chemical formula is Cu12As4S13. It is found in hydrothermal veins and contact metamorphic deposits. A closely related mineral, tetrahedrite (Cu12Sb4S13) has antimony substituting for arsenic and the t...

Tin is a chemical element in the periodic table that has the symbol Sn (L. Stannum) and atomic number 50. This silvery, malleable poor metal that is not easily oxidized in air and resists corrosion is found in many alloys and is used to coat other meta...

Tincalconite is a mineral closely related to borax, and is a secondary mineral that forms if borax is allowed to dry. The crystal shape of borax does not change during the drying process. Its formula is Na2B4O5(OH)4 - 3H2O or Na2B4O7 - 5H2O. While m...