Difference between revisions of "Mineral" - New World Encyclopedia

From New World Encyclopedia
 
(27 intermediate revisions by 6 users not shown)
Line 1: Line 1:
{{otheruses}}
+
{{Copyedited}}{{Paid}}{{Images OK}}{{Submitted}}{{Approved}}
 +
[[Category:Public]]
  
'''Minerals''' are natural compounds formed through [[geology|geological]] processes. The term "mineral" encompasses not only the material's [[chemical composition]], but also the [[Mineral structures|mineral's structure]]. Minerals range in composition from pure [[Chemical element|element]]s and simple [[salt]]s to very complex [[silicate]]s with thousands of known forms (organic compounds are usually excluded). The study of minerals is called [[mineralogy]]. [[Image:minerals.jpg|right|frame|An assortment of minerals. Photo from [http://volcanoes.usgs.gov/Products/Pglossary/mineral.html US Geological Survey].]]
+
[[Image:minerals.jpg|right|frame|An assortment of minerals. Photo from [http://volcanoes.usgs.gov/Products/Pglossary/mineral.html U.S. Geological Survey].]]
 +
'''Minerals''' are inorganic crystalline compounds formed by natural processes. They range in composition from pure [[Chemical element|element]]s and simple [[salt]]s to complex [[silicate]]s with thousands of known forms. They are identified and classified according to their physical properties and chemical compositions. Many minerals are the raw materials from which metals are extracted; others are used as gemstones. Some, such as gypsum, are constituents of cement, plaster, and paint; others, such as quartz, are important for electronics and telecommunications equipment. Unfortunately, human history is also marked by examples of people who have stolen, plundered, and fought over valuable minerals. These types of interactions with nature are a result of our distorted sense of values, and ignorance of the types of relationships that can make us truly happy.
 +
{{toc}}
  
 
== Mineral definition and classification ==
 
== Mineral definition and classification ==
  
A mineral is defined as a naturally occurring, [[inorganic]] [[solid]] with a definite [[chemical]] composition and [[crystal]]line structure. Mineral-like substances that do not strictly meet this definition are sometimes classified as [[mineraloid]]*s. Other naturally occurring substances are called ''nonminerals''. "Industrial minerals" is a market term and refers to commercially valuable, mined materials.
+
A mineral is defined as a naturally occurring, [[inorganic]] [[solid]] with a definite [[chemical]] composition and [[crystal]]line structure. Most minerals are formed through geochemical processes, but some (carbonates and phosphates) are produced by biological systems.
  
A number of minerals may be grouped together when they are closely related in chemical composition. For example, the plagioclase [[feldspar]]*s consist of a continuous series of minerals, from [[sodium]]-rich albite (NaAlSi<sub>3</sub>O<sub>8</sub>) to [[calcium]]-rich anorthite (CaAl<sub>2</sub>Si<sub>2</sub>O<sub>8</sub>), with four recognized intermediate compositions.
+
Mineral-like substances that do not strictly meet this definition are sometimes classified as ''mineraloids''. Other naturally occurring substances are called ''nonminerals''. "Industrial minerals" is a market term and refers to commercially valuable, mined materials.
 +
 
 +
Minerals that are closely related in composition and structure are grouped together. For example, the [[feldspar]] group of minerals, which make up as much as 60 percent of the [[Earth]]'s crust, can be subdivided into potassium feldspars and plagioclase feldspars. The latter subgroup consists of a continuous series of minerals, from [[sodium]]-rich albite (NaAlSi<sub>3</sub>O<sub>8</sub>) to [[calcium]]-rich anorthite (CaAl<sub>2</sub>Si<sub>2</sub>O<sub>8</sub>), with four recognized intermediate compositions.
 +
 
 +
The [[quartz]], [[mica]], and [[feldspar]] groups of minerals are common, while others have been found in only one or two locations worldwide. Over half the known mineral species are so rare that they have been found in only a handful of samples, and many are known from only one or two small grains.
 +
 
 +
[[Image:Atomic_structure_of_olivine_1.png|left|thumbnail|Atomic-scale crystal structure of olivine (magnesium iron silicate), as viewed along one axis (the ''a'' axis). Oxygen is shown in red, silicon in pink, and magnesium/iron in blue. A projection of the unit cell is indicated by the black rectangle.]]
  
 
The '''crystal structure''' of a mineral is the orderly, geometric arrangement of [[atom]]s or [[ion]]s in the mineral's internal structure. There are 14 basic crystal lattice arrangements of atoms in three dimensions, and these are referred to as the 14 "Bravais lattices." Each of these lattices can be classified into one of the six "crystal systems." All currently recognized crystal structures fit into one Bravais lattice and one crystal system. Even when the mineral grains are too small to see or are irregularly shaped, the underlying crystal structure is always periodic and can be determined by a technique known as [[X ray|X-ray]] diffraction.
 
The '''crystal structure''' of a mineral is the orderly, geometric arrangement of [[atom]]s or [[ion]]s in the mineral's internal structure. There are 14 basic crystal lattice arrangements of atoms in three dimensions, and these are referred to as the 14 "Bravais lattices." Each of these lattices can be classified into one of the six "crystal systems." All currently recognized crystal structures fit into one Bravais lattice and one crystal system. Even when the mineral grains are too small to see or are irregularly shaped, the underlying crystal structure is always periodic and can be determined by a technique known as [[X ray|X-ray]] diffraction.
  
The typical, outward appearance of a mineral is called the "crystal habit." Some crystal habits are distinctive of certain minerals, but in most cases, a mineral exhibits a variety of habits that are influenced by the growth conditions of the crystals. An inexperienced observer may be misled by a mineral's crystal habit, as the crystal system can be hidden or disguised.
+
The typical, outward appearance of a mineral is called the "crystal habit." Some crystal habits are distinctive of certain minerals, but in most cases, a mineral exhibits a variety of habits that are influenced by the growth conditions of the crystals. A mineral may show good crystal habit or form, or it may be massive, granular, or compact with only microscopically visible crystals. An inexperienced observer may be misled by a mineral's crystal habit, as the crystal system can be hidden or disguised.
 +
 
 +
Chemistry and crystal structure (and crystal habit) together define a mineral. The task of classification can range from being simple to complex. In some cases, knowledge of some properties may be sufficient for complete identification. In other cases, classification of a mineral may require more complex chemical or [[X-ray diffraction]] analyses. These methods can be costly and time-consuming, and may risk damaging the sample.
  
Chemistry and crystal structure together define a mineral. When two or more minerals have the same chemical composition but differ in crystal structure, they are known as ''polymorphs''. For example, [[pyrite]] and [[marcasite]] are both iron sulfide, but their arrangement of atoms differs. Similarly, some minerals have different chemical compositions but the same crystal structure. For example, [[halite]] (made from sodium and [[chlorine]]), [[galena]] (made from [[lead]] and [[sulfur]]), and [[periclase]] (made from [[magnesium]] and [[oxygen]]) all share the same cubic crystal structure.
+
When two or more minerals have the same chemical composition but differ in crystal structure, they are known as ''polymorphs''. For example, [[pyrite]] and [[marcasite]] are both iron sulfide, but their arrangement of atoms differs. Similarly, some minerals have different chemical compositions but the same crystal structure. For example, [[halite]] (made from sodium and [[chlorine]]), [[galena]] (made from [[lead]] and [[sulfur]]), and [[periclase]] (made from [[magnesium]] and [[oxygen]]) share the same cubic crystal structure.
  
 
Crystal structure greatly influences a mineral's physical properties. For example, both [[diamond]] and [[graphite]] are pure [[carbon]]), but graphite is very soft, while diamond is the hardest of all known minerals. The reason for this difference is that the carbon atoms in graphite are arranged into sheets that can easily slide past one another, while the carbon atoms in diamond form a strong, interlocking three-dimensional network.
 
Crystal structure greatly influences a mineral's physical properties. For example, both [[diamond]] and [[graphite]] are pure [[carbon]]), but graphite is very soft, while diamond is the hardest of all known minerals. The reason for this difference is that the carbon atoms in graphite are arranged into sheets that can easily slide past one another, while the carbon atoms in diamond form a strong, interlocking three-dimensional network.
Line 21: Line 32:
 
=== Rocks ===
 
=== Rocks ===
  
A [[Rock (geology)|rock]] is an aggregate of two or more minerals, and it may also include organic remains. In some rocks, one mineral may be predominant. For example, [[limestone]] is a [[sedimentary]] rock composed almost entirely of the mineral [[calcite]]*. Other rocks contain many minerals, and the specific minerals in a rock can vary widely.
+
A [[Rock (geology)|rock]] is an aggregate of two or more minerals, and it may also include organic remains. In some rocks, one mineral may be predominant. For example, [[limestone]] is a [[sedimentary]] rock composed almost entirely of the mineral [[calcite]]. Other rocks contain many minerals, and the specific minerals in a rock can vary widely.
  
=== Physical properties of minerals ===
+
== Physical properties ==
  
Classifying minerals can range from simple to very difficult.  
+
When identifying and classifying a mineral, the following physical properties are taken into consideration.
  
A mineral is identified and classified based on several physical and chemical properties. Some of the properties may be sufficient for full identification without equivocation. In other cases, classification of a mineral may require more complex chemical or [[X-ray diffraction]] analyses. These methods can be costly and time-consuming, and may even risk damaging the sample.
+
* ''Crystal structure and habit'', noted above.
 +
[[Image:Talc block.jpg|thumb|Talc is an extremely soft mineral, with a hardness of 1 on the Mohs scale.]]
 +
* The physical ''hardness'' (scratch resistance) of a mineral is usually measured on the Mohs scale, which ranges from 1 to 10. A mineral with a given Mohs hardness can scratch the surface of any mineral ranked lower in hardness. Certain minerals have been chosen to define the scale, as given below.
 +
::1- [[talc]]
 +
::2- [[gypsum]]
 +
::3- [[calcite]]
 +
::4- [[fluorite]]
 +
::5- [[apatite]]
 +
::6- [[orthoclase]] [[feldspar]]
 +
::7- [[quartz]]
 +
::8- [[topaz]]
 +
::9- [[corundum]]
 +
::10- [[diamond]]
 +
[[Image:GalenaFromKansas.jpg|thumb|220px|Galena (lead sulfide) has a metallic luster.]]
 +
* ''Luster'' indicates the way the mineral's surface interacts with light. It can range from metallic to glassy (vitreous) to dull.
 +
::Metallic - high reflectivity like metal (e.g., galena)
 +
::Sub-metallic - slightly less than metallic reflectivity (e.g., magnetite)
 +
::Vitreous - the luster of broken glass (e.g., quartz)
 +
::Pearly - very soft light shown by some layer silicates (e.g., talc)
 +
::Silky - soft light shown by fibrous materials (e.g., gypsum)
 +
::Dull/earthy - shown by finely crystallized minerals (e.g., kidney ore variety of hematite)
  
Physical properties commonly used are :
+
* ''Color'' indicates the mineral's appearance as observed by the naked eye. Technically, it means the color of reflected light, if the mineral is opaque, or the color of transmitted light, if the mineral is translucent.
* ''Crystal structure and habit'': See the above discussion of crystal structure. A mineral may show good crystal habit or form, or it may be massive, granular or compact with only microscopically visible crystals.
+
* <div id="Streak">''Streak'' refers to the color of the powder produced from a mineral after it has been rubbed on an unglazed porcelain ''streak plate''.</div>
* ''[[Mohs scale of mineral hardness|Hardness]]'': The physical hardness of a mineral is usually measured according to the Mohs scale. This scale is relative and goes from 1 to 10. Minerals with a given Mohs hardness can scratch the surface of any mineral that has a lower hardness than itself. The minerals that define the scale are given below:
+
* ''[[Cleavage (crystal)|Cleavage]]'' describes the way a mineral may split apart along various planes. In thin section, cleavage is visible as thin, parallel lines across a mineral.
 +
* ''Fracture'' describes how a mineral breaks when broken contrary to its natural cleavage planes. For example, a ''chonchoidal fracture'' is a smooth fracture with concentric ridges of the type shown by glass.
 +
* ''[[Specific gravity]]'' corresponds to the [[density]] of the material compared to that of water. Most minerals, including all rock-forming minerals, have a specific gravity of 2.5&ndash;3.5. Some, however, are noticeably more or less dense. For example, the specific gravity of several sulphide minerals is higher than that of the common, rock-forming minerals.
 +
* Other properties: [[fluorescence]] (response to ultraviolet light), [[magnetism]], [[radioactivity]], [[tenacity]] (response to mechanically induced changes of shape or form), and reactivity to dilute [[acid]]s.
  
1- [[talc]]
+
== Chemical properties ==
2- [[gypsum]]
 
3- [[calcite]]
 
4- [[fluorite]]
 
5- [[apatite]]
 
6- [[orthoclase]] [[feldspar]]
 
7- [[quartz]]
 
8- [[topaz]]
 
9- [[corundum]]
 
10- [[diamond]]
 
  
* ''Luster'' indicates the way a mineral's surface interacts with light and can range from dull to glassy (vitreous).
+
The classification of minerals is also based on their chemical composition. Here they are categorized by their ''[[anion]]'' groups. The list below, which follows the [[James Dwight Dana|Dana]] classification system, is in approximate order of abundance of the minerals in the Earth's [[Crust (geology)|crust]].
  
Metallic    -high reflectivity like metal, e.g. galena
+
=== Silicate class ===
 +
[[Image:MicaSheetUSGOV.jpg|thumb|left|The mica group of minerals belongs to the silicate class.]]
  
Sub-metallic -slightly less than metallic reflectivity, e.g. magnetite
+
The largest group of minerals by far are the '''[[Silicate minerals|silicates]]''' (most rocks are more than 95 percent silicates). They are composed largely of [[silicon]] and [[oxygen]], with the addition of ions such as [[aluminum]], [[magnesium]], [[iron]], and [[calcium]]. Some important rock-forming silicates include the following groups: [[feldspar]]s, [[quartz]], [[olivine]]s, [[pyroxene]]s, [[amphibole]]s, [[garnet]]s, and [[mica]]s.
  
Vitreous    -the lustre of a broken glass, e.g. quartz
+
=== Carbonate class ===
  
Pearly      -a very soft light shown by some layer silicates, e.g. talc
+
The '''[[carbonate minerals]]''' consist of those that contain the anion CO<sub>3</sub><sup>2-</sup>. They include [[calcite]] and [[aragonite]] (both calcium carbonate), [[dolomite]] (magnesium/calcium carbonate), and [[siderite]] (iron carbonate). Carbonates are commonly formed by marine organisms that secrete shells. When these organisms die, their shells settle out of the water and accumulate on the seafloor. Carbonates are also found in [[evaporite|evaporitic]] settings (for example, the [[Great Salt Lake]], [[Utah]]) and in [[karst]] regions, where the dissolution and reprecipitation of carbonates leads to the formation of [[cave]]s, [[stalactite]]s and [[stalagmite]]s. The carbonate class includes the [[nitrate]] and [[borate]] minerals.
  
Silky        -a soft light shown by fibrous materials, e.g. gypsum
+
=== Sulfate class ===
 +
[[Image:Anhydrite_HMNH1.jpg|250px|thumb|Anhydrite is a sulfate mineral (anhydrous calcium sulfate). This sample came from Chihuahua, Mexico.]]
  
Dull/earthy  -shown by finely crystallized minerals, e.g. the kidney ore variety of hematite
+
The '''[[sulfate]]s''' contain the sulfate anion, SO<sub>4</sub><sup>2-</sup>. Sulfates commonly form in [[evaporite|evaporitic]] settings, where highly saline waters slowly evaporate, allowing the formation of sulfates and halides at the water-sediment interface. Sulfates also occur in [[hydrothermal]] vein systems as gangue minerals, along with [[sulfide]] [[ore]] minerals. Another occurrence is as secondary [[oxidation]] products of original sulfide minerals. Common sulfates include [[anhydrite]] (calcium sulfate), [[celestite]] (strontium sulfate), [[barite]] (barium sulfate), and [[gypsum]] (hydrated calcium sulfate). The sulfate class also includes the [[chromate]], [[molybdate]], [[selenate]], [[sulfite]], [[tellurate]], and [[tungstate]] minerals.
  
* ''Color'' indicates the appearance of the mineral in reflected light or transmitted light for translucent minerals (i.e. what it looks like to the naked eye).
+
=== Halide class ===
* <div id="Streak">''Streak'' refers to the color of the powder a mineral leaves after rubbing it on an unglazed porcelain ''streak plate''.</div>
 
* ''[[Cleavage (crystal)|Cleavage]]'' describes the way a mineral may split apart along various planes.  In thin section, cleavage is visible as thin parallel lines across a mineral.
 
* ''Fracture'' describes how a mineral breaks when broken contrary to its natural cleavage planes, e.g. a ''chonchoidal fracture'' is a smooth fracture with concentric ridges of the type shown by glass.
 
* ''[[Specific gravity]]'' relates the mineral [[mass]] to the mass of an equal volume of water, namely the [[density]] of the material. While most minerals, including all the rock-forming minerals, have a specific gravity of 2.5 - 3.5, a few are noticably more or less dense, e.g. several sulphide minerals have high specific gravity compared to the common rock-forming minerals.
 
* Other properties: [[fluorescence]] (response to ultraviolet light), [[magnetism]], [[radioactivity]], [[tenacity]] (response to mechanical induced changes of shape or form), and reactivity to dilute [[acid]]s.
 
  
=== Chemical properties of minerals ===
+
The '''[[halide]]s''' are a group of minerals that form [[salt]]s such as [[fluorite]] (calcium fluoride), [[halite]] (sodium chloride), [[sylvite]] (potassium chloride), and [[sal ammoniac]] (ammonium chloride). Like the sulfates, halides are commonly found in evaporitic settings such as [[Playa|playa lake]]s (lakebeds that are usually dry) and landlocked seas, such as the [[Dead Sea]] and Great Salt Lake. The halide class includes the [[fluoride]], [[chloride]], and [[iodide]] minerals.
Minerals may be classified according to chemical composition. They are here categorized by [[anion]] group. The list below is in approximate order of their abundance in the Earth's [[Crust (geology)|crust]]. The list follows the [[James Dwight Dana|Dana]] classification system.
 
  
==== Silicate class ====
+
=== Oxide class ===
The largest group of minerals by far are the '''[[Silicate minerals|silicates]]''' (most rocks are >95% silicates), which are composed largely of [[silicon]] and [[oxygen]], with the addition of ions such as [[aluminium]], [[magnesium]], [[iron]], and [[calcium]].  Some important rock-forming silicates include the [[feldspar]]s, [[quartz]], [[olivine]]s, [[pyroxene]]s, [[amphibole]]s, [[garnet]]s, and [[mica]]s.
 
  
==== Carbonate class ====
+
'''[[Oxide]]s''' are extremely important in [[mining]], as they form many of the ores from which valuable metals are extracted. They commonly occur as precipitates close to the Earth's surface, [[oxidation]] products of other minerals in the near-surface [[weathering]] zone, and as accessory minerals in igneous rocks of the crust and [[Mantle (geology)|mantle]]. Common oxides include [[hematite]] (iron oxide), [[magnetite]] (iron oxide), [[chromite]] (chromium oxide), [[spinel]] (magnesium aluminium oxide, a common component of the mantle), [[rutile]] (titanium dioxide), and [[ice]] (hydrogen oxide). The oxide class includes the [[hydroxide]] minerals.
The '''[[carbonate minerals]]''' consist of those minerals containing the anion (CO<sub>3</sub>)<sup>2-</sup> and include [[calcite]] and [[aragonite]] (both calcium carbonate), [[dolomite]] (magnesium/calcium carbonate) and [[siderite]] (iron carbonate).  Carbonates are commonly deposited in marine settings when the shells of dead [[plankton|planktonic]] life settle and accumulate on the sea floor. Carbonates are also found in [[evaporite|evaporitic]] settings (e.g. the [[Great Salt Lake]], [[Utah]]) and also in [[karst]] regions, where the dissolution and reprecipitation of carbonates leads to the formation of [[cave]]s, [[stalactite]]s and [[stalagmite]]s. The carbonate class also includes the [[nitrate]] and [[borate]] minerals.
 
  
==== Sulfate class ====
+
=== Sulfide class ===
'''[[Sulfate]]s''' all contain the sulfate anion, SO<sub>4</sub><sup>2-</sup>. Sulfates commonly form in [[evaporite|evaporitic]] settings where highly saline waters slowly evaporate, allowing the formation of both sulfates and halides at the water-sediment interface. Sulfates also occur in [[hydrothermal]] vein systems as gangue minerals along with [[sulfide]] [[ore]] minerals. Another occurrence is as secondary [[oxidation]] products of original sulfide minerals. Common sulfates include [[anhydrite]] (calcium sulfate), [[celestite]] (strontium sulfate), [[barite]] (barium sulfate), and [[gypsum]] (hydrated calcium sulfate). The sulfate class also includes the [[chromate]], [[molybdate]], [[selenate]], [[sulfite]], [[tellurate]], and [[tungstate]] minerals.
+
[[Image:Pyrite foolsgold.jpg|250px|thumb|left|Pyrite (iron disulfide), also known as fool's gold, is a sulfide mineral. Shown here is a mass of intergrown pyrite crystals.]]
  
==== Halide class ====
+
Many '''[[sulfide]]s''' are economically important as metal ores. Common sulfides include [[pyrite]] (iron sulfide, also known as ''fool's gold''), [[chalcopyrite]] (copper iron sulfide), [[pentlandite]] (nickel iron sulfide), and galena (lead sulfide). The sulfide class also includes the [[selenide]]s, [[telluride]]s, [[arsenide]]s, [[antimonide]]s, bismuthinides, and sulfo salts (containing sulfide and a second anion such as arsenide).
The '''[[halide]]s''' are the group of minerals forming the natural [[salt]]s and include [[fluorite]] (calcium fluoride), [[halite]] (sodium chloride), [[sylvite]] (potassium chloride), and [[sal ammoniac]] (ammonium chloride). Halides, like sulfates, are commonly found in evaporitic settings such as [[Playa|playa lake]]s and landlocked seas such as the [[Dead Sea]] and Great Salt Lake. The halide class includes the [[fluoride]], [[chloride]], and [[iodide]] minerals.
 
  
==== Oxide class ====
+
=== Phosphate class ===
'''[[Oxide]]s''' are extremely important in [[mining]] as they form many of the ores from which valuable metals can be extracted. They commonly occur as precipitates close to the Earth's surface, [[oxidation]] products of other minerals in the near surface [[weathering]] zone, and as accessory minerals in igneous rocks of the crust and [[Mantle (geology)|mantle]]. Common oxides include [[hematite]] (iron oxide), [[magnetite]] (iron oxide), [[chromite]] (chromium oxide), [[spinel]] (magnesium aluminium oxide - a common component of the mantle), [[rutile]] (titanium dioxide), and [[ice]] (hydrogen oxide). The oxide class includes the oxide and the [[hydroxide]] minerals.
 
  
==== Sulfide class ====
+
The '''[[phosphate mineral]]''' group includes any mineral in which the anion takes the tetrahedral form AO<sub>4</sub><sup>-n</sup>, where A can be [[phosphorus]], [[antimony]], [[arsenic]] or [[vanadium]]. The most common group of phosphates is apatite, consisting mainly of hydroxyapatite (hydroxylapatite), fluorapatite, and chlorapatite. Hydroxyapatite is an important [[biology|biological]] mineral found in the teeth and bones of many animals.
  
Many '''[[sulfide]]s''' are economically important as metal ores.  Common sulfides include [[pyrite]] (iron sulfide - commonly known as ''fools' gold''), [[chalcopyrite]] (copper iron sulfide), [[pentlandite]] (nickel iron sulfide), and galena (lead sulfide). The sulfide class also includes the [[selenide]]s, the [[telluride]]s, the [[arsenide]]s, the [[antimonide]]s, the bismuthinides, and the sulfosalts (sulfur and a second anion such as arsenic).
+
=== Element class ===
  
==== Phosphate class ====
+
The '''element''' group includes metals, metalloids, and nonmetals. Minerals in this group include gold, silver, copper, antimony, bismuth, graphite, and sulfur. This group also includes naturally occurring alloys (such as [[electrum]], an alloy of gold and silver), phosphides, silicides, nitrides, and carbides (which are found naturally in a few, rare meteorites).
  
The '''[[phosphate mineral]]''' group actually includes any mineral with a tetrahedral unit AO<sub>4</sub> where A can be [[phosphorus]], [[antimony]], [[arsenic]] or [[vanadium]].  By far the most common phosphate is [[apatite]] which is an important [[biology|biological]] mineral found in teeth and bones of many animals. The phosphate class includes the phosphate, [[arsenate]], [[vanadate]], and [[antimonate]] minerals.
+
== Uses ==
  
==== Element class ====
+
Minerals are extremely valuable for a wide variety of uses. Many of them are ores from which key elements are purified. Others are used as ornamental stones. Examples of the uses of some minerals are given below.
 
+
* Chalcopyrite (copper iron sulfide) is an important ore of copper.
The Elemental group includes metals and intermetallic elements (gold, silver, copper), semi-metals and non-metals (antimony, bismuth, graphite, sulfur). This group also includes natural alloys, such as [[electrum]] (a natural alloy of gold and silver), phosphides, silicides, nitrides and carbides (which are usually only found naturally in a few rare meteorites).
+
* Chromite (iron magnesium chromium oxide) is the main ore of chromium and is also used as a refractory material.
 +
* Diamond (a carbon allotrope) is mined for its high value as a gemstone, but it is also an excellent abrasive.
 +
* Dolomite (calcium magnesium carbonate) is used as an ornamental stone and for cement manufacture.
 +
* Fluorite (calcium fluoride) is used to make opalescent [[glass]], enamels for cooking utensils, and hydrofluoric acid, which etches glass.
 +
* Galena (lead sulfide) is a common ore of lead.
 +
* Gypsum (calcium sulfate dihydrate) is a constituent of blackboard chalk, cement, plaster, paint filler, pharmaceuticals, toothpaste, and more. It is also a calcium additive in breads and cereals.
 +
* Hematite (iron oxide) is the main ore of iron.
 +
* Mica (a group of silicates) is useful for making capacitors and electrical insulators.
 +
* Orthoclase feldspar (potassium aluminum silicate) is used to manufacture porcelain and is a component of scouring powder.
 +
* Pyrite (iron disulfide, fool's gold) is used in making jewelry and producing sulfur dioxide and sulfuric acid.
 +
* Quartz (silicon dioxide, with many varieties) has many uses, such as to make crystal oscillators for wristwatches and [[integrated circuits]], precision mirrors for [[telescope]]s, and [[optical fiber]]s for telecommunications. Several varieties of quartz are used as gemstones.
  
 
==See also==
 
==See also==
* [[List of minerals|A list of minerals]] with associated Wikipedia articles
 
* [[List of minerals (complete)|A comprehensive list of minerals]]
 
* [[Industrial minerals]]
 
 
* [[Mineral water]], water containing minerals or other dissolved substances that alter its taste or give it therapeutic value
 
* [[Mineral water]], water containing minerals or other dissolved substances that alter its taste or give it therapeutic value
* [[Mineral wool]]
 
 
* [[Mining]]
 
* [[Mining]]
* [[Norman L. Bowen]]
 
 
* [[Quarry]]
 
* [[Quarry]]
 
* [[Dietary mineral]]
 
* [[Dietary mineral]]
  
 
== External links ==
 
== External links ==
{{Commonscat|Minerals}}
+
All links retrieved November 9, 2022.
*[http://mineral.galleries.com/minerals/by_name.htm Mineral gallery]
 
*[http://www.minerals.net/index.htm Minerals.net]
 
*[http://www.DetoxIY.co.uk Information on minerals]
 
*[http://www.mindat.org/index.php mindat.org mineral database]
 
*[http://webmineral.com Webmineral.com]
 
*[http://www.minerant.org/databases.html a directory of on-line databases related to mineralogy and crystallography]
 
 
 
  
== References ==
+
*[http://www.mindat.org/index.php mineral database] ''Mindat.org''
*[http://volcanoes.usgs.gov/Products/Pglossary/mineral.html Photo glossary of volcano terms from the USGS Volcano Hazards Program]
+
*[http://webmineral.com Mineralogy Database] ''Webmineral.com''
  
 
[[Category:Physical sciences]]
 
[[Category:Physical sciences]]
 
[[Category:Earth sciences]]
 
[[Category:Earth sciences]]
 
[[Category:Geology]]
 
[[Category:Geology]]
[[Category:Mineralogy]]
 
[[Category:Minerals|*]]
 
  
{{credit|56301785}}
+
{{credit8|Mineral|56301785|Feldspar|57213250|Gypsum|57198117|Fluorite|53002625|Dolomite|57149566|Mica|55131960|Pyrite|57252339|Quartz|56594204}}

Latest revision as of 18:48, 9 November 2022


An assortment of minerals. Photo from U.S. Geological Survey.

Minerals are inorganic crystalline compounds formed by natural processes. They range in composition from pure elements and simple salts to complex silicates with thousands of known forms. They are identified and classified according to their physical properties and chemical compositions. Many minerals are the raw materials from which metals are extracted; others are used as gemstones. Some, such as gypsum, are constituents of cement, plaster, and paint; others, such as quartz, are important for electronics and telecommunications equipment. Unfortunately, human history is also marked by examples of people who have stolen, plundered, and fought over valuable minerals. These types of interactions with nature are a result of our distorted sense of values, and ignorance of the types of relationships that can make us truly happy.

Mineral definition and classification

A mineral is defined as a naturally occurring, inorganic solid with a definite chemical composition and crystalline structure. Most minerals are formed through geochemical processes, but some (carbonates and phosphates) are produced by biological systems.

Mineral-like substances that do not strictly meet this definition are sometimes classified as mineraloids. Other naturally occurring substances are called nonminerals. "Industrial minerals" is a market term and refers to commercially valuable, mined materials.

Minerals that are closely related in composition and structure are grouped together. For example, the feldspar group of minerals, which make up as much as 60 percent of the Earth's crust, can be subdivided into potassium feldspars and plagioclase feldspars. The latter subgroup consists of a continuous series of minerals, from sodium-rich albite (NaAlSi3O8) to calcium-rich anorthite (CaAl2Si2O8), with four recognized intermediate compositions.

The quartz, mica, and feldspar groups of minerals are common, while others have been found in only one or two locations worldwide. Over half the known mineral species are so rare that they have been found in only a handful of samples, and many are known from only one or two small grains.

Atomic-scale crystal structure of olivine (magnesium iron silicate), as viewed along one axis (the a axis). Oxygen is shown in red, silicon in pink, and magnesium/iron in blue. A projection of the unit cell is indicated by the black rectangle.

The crystal structure of a mineral is the orderly, geometric arrangement of atoms or ions in the mineral's internal structure. There are 14 basic crystal lattice arrangements of atoms in three dimensions, and these are referred to as the 14 "Bravais lattices." Each of these lattices can be classified into one of the six "crystal systems." All currently recognized crystal structures fit into one Bravais lattice and one crystal system. Even when the mineral grains are too small to see or are irregularly shaped, the underlying crystal structure is always periodic and can be determined by a technique known as X-ray diffraction.

The typical, outward appearance of a mineral is called the "crystal habit." Some crystal habits are distinctive of certain minerals, but in most cases, a mineral exhibits a variety of habits that are influenced by the growth conditions of the crystals. A mineral may show good crystal habit or form, or it may be massive, granular, or compact with only microscopically visible crystals. An inexperienced observer may be misled by a mineral's crystal habit, as the crystal system can be hidden or disguised.

Chemistry and crystal structure (and crystal habit) together define a mineral. The task of classification can range from being simple to complex. In some cases, knowledge of some properties may be sufficient for complete identification. In other cases, classification of a mineral may require more complex chemical or X-ray diffraction analyses. These methods can be costly and time-consuming, and may risk damaging the sample.

When two or more minerals have the same chemical composition but differ in crystal structure, they are known as polymorphs. For example, pyrite and marcasite are both iron sulfide, but their arrangement of atoms differs. Similarly, some minerals have different chemical compositions but the same crystal structure. For example, halite (made from sodium and chlorine), galena (made from lead and sulfur), and periclase (made from magnesium and oxygen) share the same cubic crystal structure.

Crystal structure greatly influences a mineral's physical properties. For example, both diamond and graphite are pure carbon), but graphite is very soft, while diamond is the hardest of all known minerals. The reason for this difference is that the carbon atoms in graphite are arranged into sheets that can easily slide past one another, while the carbon atoms in diamond form a strong, interlocking three-dimensional network.

There are currently just over 4,000 known minerals, according to the International Mineralogical Association, which is responsible for the approval and naming of newly discovered mineral species.

Rocks

A rock is an aggregate of two or more minerals, and it may also include organic remains. In some rocks, one mineral may be predominant. For example, limestone is a sedimentary rock composed almost entirely of the mineral calcite. Other rocks contain many minerals, and the specific minerals in a rock can vary widely.

Physical properties

When identifying and classifying a mineral, the following physical properties are taken into consideration.

  • Crystal structure and habit, noted above.
Talc is an extremely soft mineral, with a hardness of 1 on the Mohs scale.
  • The physical hardness (scratch resistance) of a mineral is usually measured on the Mohs scale, which ranges from 1 to 10. A mineral with a given Mohs hardness can scratch the surface of any mineral ranked lower in hardness. Certain minerals have been chosen to define the scale, as given below.
1- talc
2- gypsum
3- calcite
4- fluorite
5- apatite
6- orthoclase feldspar
7- quartz
8- topaz
9- corundum
10- diamond
Galena (lead sulfide) has a metallic luster.
  • Luster indicates the way the mineral's surface interacts with light. It can range from metallic to glassy (vitreous) to dull.
Metallic - high reflectivity like metal (e.g., galena)
Sub-metallic - slightly less than metallic reflectivity (e.g., magnetite)
Vitreous - the luster of broken glass (e.g., quartz)
Pearly - very soft light shown by some layer silicates (e.g., talc)
Silky - soft light shown by fibrous materials (e.g., gypsum)
Dull/earthy - shown by finely crystallized minerals (e.g., kidney ore variety of hematite)
  • Color indicates the mineral's appearance as observed by the naked eye. Technically, it means the color of reflected light, if the mineral is opaque, or the color of transmitted light, if the mineral is translucent.
  • Streak refers to the color of the powder produced from a mineral after it has been rubbed on an unglazed porcelain streak plate.
  • Cleavage describes the way a mineral may split apart along various planes. In thin section, cleavage is visible as thin, parallel lines across a mineral.
  • Fracture describes how a mineral breaks when broken contrary to its natural cleavage planes. For example, a chonchoidal fracture is a smooth fracture with concentric ridges of the type shown by glass.
  • Specific gravity corresponds to the density of the material compared to that of water. Most minerals, including all rock-forming minerals, have a specific gravity of 2.5–3.5. Some, however, are noticeably more or less dense. For example, the specific gravity of several sulphide minerals is higher than that of the common, rock-forming minerals.
  • Other properties: fluorescence (response to ultraviolet light), magnetism, radioactivity, tenacity (response to mechanically induced changes of shape or form), and reactivity to dilute acids.

Chemical properties

The classification of minerals is also based on their chemical composition. Here they are categorized by their anion groups. The list below, which follows the Dana classification system, is in approximate order of abundance of the minerals in the Earth's crust.

Silicate class

The mica group of minerals belongs to the silicate class.

The largest group of minerals by far are the silicates (most rocks are more than 95 percent silicates). They are composed largely of silicon and oxygen, with the addition of ions such as aluminum, magnesium, iron, and calcium. Some important rock-forming silicates include the following groups: feldspars, quartz, olivines, pyroxenes, amphiboles, garnets, and micas.

Carbonate class

The carbonate minerals consist of those that contain the anion CO32-. They include calcite and aragonite (both calcium carbonate), dolomite (magnesium/calcium carbonate), and siderite (iron carbonate). Carbonates are commonly formed by marine organisms that secrete shells. When these organisms die, their shells settle out of the water and accumulate on the seafloor. Carbonates are also found in evaporitic settings (for example, the Great Salt Lake, Utah) and in karst regions, where the dissolution and reprecipitation of carbonates leads to the formation of caves, stalactites and stalagmites. The carbonate class includes the nitrate and borate minerals.

Sulfate class

Anhydrite is a sulfate mineral (anhydrous calcium sulfate). This sample came from Chihuahua, Mexico.

The sulfates contain the sulfate anion, SO42-. Sulfates commonly form in evaporitic settings, where highly saline waters slowly evaporate, allowing the formation of sulfates and halides at the water-sediment interface. Sulfates also occur in hydrothermal vein systems as gangue minerals, along with sulfide ore minerals. Another occurrence is as secondary oxidation products of original sulfide minerals. Common sulfates include anhydrite (calcium sulfate), celestite (strontium sulfate), barite (barium sulfate), and gypsum (hydrated calcium sulfate). The sulfate class also includes the chromate, molybdate, selenate, sulfite, tellurate, and tungstate minerals.

Halide class

The halides are a group of minerals that form salts such as fluorite (calcium fluoride), halite (sodium chloride), sylvite (potassium chloride), and sal ammoniac (ammonium chloride). Like the sulfates, halides are commonly found in evaporitic settings such as playa lakes (lakebeds that are usually dry) and landlocked seas, such as the Dead Sea and Great Salt Lake. The halide class includes the fluoride, chloride, and iodide minerals.

Oxide class

Oxides are extremely important in mining, as they form many of the ores from which valuable metals are extracted. They commonly occur as precipitates close to the Earth's surface, oxidation products of other minerals in the near-surface weathering zone, and as accessory minerals in igneous rocks of the crust and mantle. Common oxides include hematite (iron oxide), magnetite (iron oxide), chromite (chromium oxide), spinel (magnesium aluminium oxide, a common component of the mantle), rutile (titanium dioxide), and ice (hydrogen oxide). The oxide class includes the hydroxide minerals.

Sulfide class

Pyrite (iron disulfide), also known as fool's gold, is a sulfide mineral. Shown here is a mass of intergrown pyrite crystals.

Many sulfides are economically important as metal ores. Common sulfides include pyrite (iron sulfide, also known as fool's gold), chalcopyrite (copper iron sulfide), pentlandite (nickel iron sulfide), and galena (lead sulfide). The sulfide class also includes the selenides, tellurides, arsenides, antimonides, bismuthinides, and sulfo salts (containing sulfide and a second anion such as arsenide).

Phosphate class

The phosphate mineral group includes any mineral in which the anion takes the tetrahedral form AO4-n, where A can be phosphorus, antimony, arsenic or vanadium. The most common group of phosphates is apatite, consisting mainly of hydroxyapatite (hydroxylapatite), fluorapatite, and chlorapatite. Hydroxyapatite is an important biological mineral found in the teeth and bones of many animals.

Element class

The element group includes metals, metalloids, and nonmetals. Minerals in this group include gold, silver, copper, antimony, bismuth, graphite, and sulfur. This group also includes naturally occurring alloys (such as electrum, an alloy of gold and silver), phosphides, silicides, nitrides, and carbides (which are found naturally in a few, rare meteorites).

Uses

Minerals are extremely valuable for a wide variety of uses. Many of them are ores from which key elements are purified. Others are used as ornamental stones. Examples of the uses of some minerals are given below.

  • Chalcopyrite (copper iron sulfide) is an important ore of copper.
  • Chromite (iron magnesium chromium oxide) is the main ore of chromium and is also used as a refractory material.
  • Diamond (a carbon allotrope) is mined for its high value as a gemstone, but it is also an excellent abrasive.
  • Dolomite (calcium magnesium carbonate) is used as an ornamental stone and for cement manufacture.
  • Fluorite (calcium fluoride) is used to make opalescent glass, enamels for cooking utensils, and hydrofluoric acid, which etches glass.
  • Galena (lead sulfide) is a common ore of lead.
  • Gypsum (calcium sulfate dihydrate) is a constituent of blackboard chalk, cement, plaster, paint filler, pharmaceuticals, toothpaste, and more. It is also a calcium additive in breads and cereals.
  • Hematite (iron oxide) is the main ore of iron.
  • Mica (a group of silicates) is useful for making capacitors and electrical insulators.
  • Orthoclase feldspar (potassium aluminum silicate) is used to manufacture porcelain and is a component of scouring powder.
  • Pyrite (iron disulfide, fool's gold) is used in making jewelry and producing sulfur dioxide and sulfuric acid.
  • Quartz (silicon dioxide, with many varieties) has many uses, such as to make crystal oscillators for wristwatches and integrated circuits, precision mirrors for telescopes, and optical fibers for telecommunications. Several varieties of quartz are used as gemstones.

See also

  • Mineral water, water containing minerals or other dissolved substances that alter its taste or give it therapeutic value
  • Mining
  • Quarry
  • Dietary mineral

External links

All links retrieved November 9, 2022.

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

The history of this article since it was imported to New World Encyclopedia:

Note: Some restrictions may apply to use of individual images which are separately licensed.