rv: You are violating the MoS. Please stop or I will be forced to call for arbitration. |
I've noticed what you are up to, Darrien. You violate the MoS by changing to Yank spellings, then claim that people changing them back are committing your crime.Do you contribute anything, chauvinist? |
||
Line 17: | Line 17: | ||
A '''[[crystal structure]]''' refers to the orderly geometric spatial arrangement of atoms in the internal structure of the mineral. There are 14 basic lattice arrangements of atoms in three dimensions in the six crystal systems, and all crystal structures currently recognized fit in one of these 14 arrangements. This [[crystal structure]] is based on regular internal atomic or ionic arrangement that is often visible on the macroscopic scale as the mineral form. Even when the mineral grains are too small to see or are irregularly shaped externally the crystal structure can be determined by [[x-ray]] analysis and/or [[optical]] [[microscopy]]. |
A '''[[crystal structure]]''' refers to the orderly geometric spatial arrangement of atoms in the internal structure of the mineral. There are 14 basic lattice arrangements of atoms in three dimensions in the six crystal systems, and all crystal structures currently recognized fit in one of these 14 arrangements. This [[crystal structure]] is based on regular internal atomic or ionic arrangement that is often visible on the macroscopic scale as the mineral form. Even when the mineral grains are too small to see or are irregularly shaped externally the crystal structure can be determined by [[x-ray]] analysis and/or [[optical]] [[microscopy]]. |
||
Chemistry and crystal structure define together a mineral. In fact, two or more minerals may have the same chemical composition, but different crystal structures (these are known as ''polymorphs''). For example, [[pyrite]] and [[marcasite]] are both iron |
Chemistry and crystal structure define together a mineral. In fact, two or more minerals may have the same chemical composition, but different crystal structures (these are known as ''polymorphs''). For example, [[pyrite]] and [[marcasite]] are both iron sulphide. Similarly, some minerals have different chemical compositions, but the same crystal structure: for example, [[halite]] (made from sodium and chlorine), [[galena (mineral)|galena]] - made from lead and sulphur) and [[periclase]] (made from magnesium and oxygen) all share the same cubic crystal structure. |
||
Crystal structure influences greatly a mineral's physical properties. For example, though diamond and graphite have the same composition (both are pure [[carbon]]), [[graphite]] is very soft, while [[diamond]] is the hardest of all minerals. |
Crystal structure influences greatly a mineral's physical properties. For example, though diamond and graphite have the same composition (both are pure [[carbon]]), [[graphite]] is very soft, while [[diamond]] is the hardest of all minerals. |
||
Line 52: | Line 52: | ||
The [[carbonate]]s 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 [[stalactite|stalagmites]]. |
The [[carbonate]]s 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 [[stalactite|stalagmites]]. |
||
==== |
==== Sulphates ==== |
||
[[ |
[[Sulphate]]s all contain the sulphate cation, in the form SO<sub>4</sub>. Sulphates commonly form in [[evaporite|evaporitic]] settings where highly saline waters slowly evaporate, allowing the formation of both sulphates and halides (q.v.) at the water-sediment interface. Common sulphates include [[anhydrite]] (calcium sulphate), [[celestine]] (strontium sulphate) and [[gypsum]] (hydrated calcium sulphate). |
||
==== Halides ==== |
==== Halides ==== |
||
The [[halide]]s are the group of minerals forming the natural [[salt]]s and include [[fluoride]], common salt (known as [[halite]]) and [[sal ammoniac]] (ammonium chloride). Halides, like |
The [[halide]]s are the group of minerals forming the natural [[salt]]s and include [[fluoride]], common salt (known as [[halite]]) and [[sal ammoniac]] (ammonium chloride). Halides, like sulphates, are commonly found in evaporitic settings such as [[playa lake]]s and landlocked seas (e.g. the [[Red Sea]]). |
||
==== Oxides ==== |
==== Oxides ==== |
||
[[Oxide]]s are extremely important in [[mining]] as they form the ores from which valuable metals can be extracted. They thus commonly occur as precipitates close to the Earth's surface. Common oxides include [[haematite]] (iron oxide), [[spinel]] (magnesium aluminium oxide - a common component of the [[earth's mantle|mantle]]) and [[ice]] (hydrogen oxide!). |
[[Oxide]]s are extremely important in [[mining]] as they form the ores from which valuable metals can be extracted. They thus commonly occur as precipitates close to the Earth's surface. Common oxides include [[haematite]] (iron oxide), [[spinel]] (magnesium aluminium oxide - a common component of the [[earth's mantle|mantle]]) and [[ice]] (hydrogen oxide!). |
||
==== |
==== Sulphides ==== |
||
Many [[ |
Many [[sulphide]]s are also economically important as metal ores. Common sulphides include [[pyrite]] (iron sulphide - commonly known as ''fools' gold''), [[chalcopyrite]] (copper iron sulphide) and [[galena (mineral)|galena]] (lead sulphide). |
||
==== Phosphates ==== |
==== Phosphates ==== |
||
Line 68: | Line 68: | ||
==== Elements ==== |
==== Elements ==== |
||
[[Elements]] group includes metals and intermetallic elements (gold, silver, copper), semi-metals and non-metals (antimony, bismuth, graphite, |
[[Elements]] group includes metals and intermetallic elements (gold, silver, copper), semi-metals and non-metals (antimony, bismuth, graphite, sulphur). 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). |
||
== Dietary mineral == |
== Dietary mineral == |
Revision as of 12:40, 2 October 2004
Minerals are natural compounds formed through geological processes. The term "mineral" encompasses not only the material's chemical composition but also the Mineral structures. Minerals range in composition from elements and simple salts to very complex silicates (with most organic compounds usually excluded), with thousands of known forms. The study of minerals is called mineralogy.
Photo from US Geological Survey |
What is a mineral ?
To be classified as a "true" mineral, a substance must be a solid and have a crystal structure. It must also be a naturally occurring homogenous substance with a defined chemical composition. The chemical composition may vary between end members of a mineral system. For example the plagioclase feldspars comprise a continuous series from sodium rich albite (NaAlSi3O8) to calcium rich anorthite (CaAl2Si2O8) with four recognized intermediate compositions between. Mineral-like substances that don't strictly meet the definition are sometimes classified as mineraloids.
A crystal structure refers to the orderly geometric spatial arrangement of atoms in the internal structure of the mineral. There are 14 basic lattice arrangements of atoms in three dimensions in the six crystal systems, and all crystal structures currently recognized fit in one of these 14 arrangements. This crystal structure is based on regular internal atomic or ionic arrangement that is often visible on the macroscopic scale as the mineral form. Even when the mineral grains are too small to see or are irregularly shaped externally the crystal structure can be determined by x-ray analysis and/or optical microscopy.
Chemistry and crystal structure define together a mineral. In fact, two or more minerals may have the same chemical composition, but different crystal structures (these are known as polymorphs). For example, pyrite and marcasite are both iron sulphide. 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 sulphur) and periclase (made from magnesium and oxygen) all share the same cubic crystal structure.
Crystal structure influences greatly a mineral's physical properties. For example, though diamond and graphite have the same composition (both are pure carbon), graphite is very soft, while diamond is the hardest of all minerals.
There are currently just over 4,000 known minerals, according to the International Mineralogical Association, which is responsible for the approval of and naming of new mineral species found in nature.
Minerals and rocks
Minerals must be distinguished from rocks. A mineral is a chemical compound with a given composition and a defined crystal structure. A rock is a mixture of one or several minerals, in varying proportions.
The specific minerals in a rock vary a lot. Some minerals, like quartz, mica or feldspar are common, while others have been found in only one or two locations worldwide. Over half of the mineral species known are so rare that they have only been found in a handful of samples, and many are known from only one or two small grains.
Physical properties of minerals
There are just over 4,000 different mineral species known, and classifying them can range from simple (for a couple of hundred) to very difficult. A mineral can be identified by several physical properties, some of them being sufficient for full identification without equivocation. In other cases, minerals can only be classified by more complex analyses chemical analysis and X-ray diffraction, which however, can be costly, time-consuming, and even risk damaging the sample.
Physical properties commonly used are :
- Hardness: the physical hardness of a mineral is usually measured according to the Mohs scale of mineral hardness.
- Luster indicates the way a mineral's surface interacts with light and can range from dull to glassy (vitreous).
- Color indicates the appearance of the mineral in reflected light (i.e. what it looks like to the naked eye).
- Cleavage describe the way a mineral may come apart or cleave in different ways. In thin sections, cleavage is visible as thin lines across a mineral.
- Fracture describes how a mineral breaks other than along natural cleavage planes.
- Specific gravity relates the mineral weight to the weight of an equal volume of water.
- Other properties: fluorescence (response to ultraviolet light), magnetism, radioactivity, tenacity (response to mechanical induced changes of shape or form).
Chemical properties of 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.
Silicates
The largest group of minerals by far are the silicates, which are composed largely of silicon and oxygen, with the addition of ions such as magnesium, iron and calcium. Some important rock-forming silicates include the feldspars, quartz, olivines, pyroxenes, garnets and micas.
Carbonates
The carbonates consist of those minerals containing the anion (CO3)2- 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 planktonic life settle and accumulate on the sea floor. Carbonates are also found in 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 caves, stalactites and stalagmites.
Sulphates
Sulphates all contain the sulphate cation, in the form SO4. Sulphates commonly form in evaporitic settings where highly saline waters slowly evaporate, allowing the formation of both sulphates and halides (q.v.) at the water-sediment interface. Common sulphates include anhydrite (calcium sulphate), celestine (strontium sulphate) and gypsum (hydrated calcium sulphate).
Halides
The halides are the group of minerals forming the natural salts and include fluoride, common salt (known as halite) and sal ammoniac (ammonium chloride). Halides, like sulphates, are commonly found in evaporitic settings such as playa lakes and landlocked seas (e.g. the Red Sea).
Oxides
Oxides are extremely important in mining as they form the ores from which valuable metals can be extracted. They thus commonly occur as precipitates close to the Earth's surface. Common oxides include haematite (iron oxide), spinel (magnesium aluminium oxide - a common component of the mantle) and ice (hydrogen oxide!).
Sulphides
Many sulphides are also economically important as metal ores. Common sulphides include pyrite (iron sulphide - commonly known as fools' gold), chalcopyrite (copper iron sulphide) and galena (lead sulphide).
Phosphates
The phosphate group actually includes any mineral with a tetrahedral unit AO4 where A can be phosphorus, antimony, arsenic or vanadium. By far the most common phosphate is apatite which is an important biological mineral found in teeth and bones of many animals.
Elements
Elements group includes metals and intermetallic elements (gold, silver, copper), semi-metals and non-metals (antimony, bismuth, graphite, sulphur). 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).
Dietary mineral
Dietary mineral refers to inorganic compounds necessary for life and good nutrition.
Some of these are scientific minerals as salt; others are elements, as potassium, calcium, iron, zinc, magnesium, copper.
These can be naturally occurring in food or added in elemental or mineral form to food, as calcium carbonate, iron fillings, etc.
Some of these additives are from natural sources as ground oyster shells for calcium carbonate.
Sometimes minerals are added to the diet separately from food, as vitamin and mineral supplements and in dirt eating, called pica or geophagy.