| Revision as of 13:59, 16 February 2003 view sourceCferrero (talk | contribs)493 editsm added external link← Previous edit | Revision as of 09:26, 4 March 2003 view source Cferrero (talk | contribs)493 edits cleaned up a bit + added stuff about chemical classificationsNext edit → | ||
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| '''Minerals''' are natural compounds formed through ] processes. The term "mineral" encompasses not only the material's '']'' but also the '']''. Minerals range in composition from elements and simple salts to very complex ]s (with most organic compounds usually excluded), with thousands of known forms. | '''Minerals''' are natural compounds formed through ] processes. The term "mineral" encompasses not only the material's '']'' but also the '']''. Minerals range in composition from elements and simple salts to very complex ]s (with most organic compounds usually excluded), with thousands of known forms. The study of minerals is called ]. | ||
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| ⚫ | ] | ||
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| ⚫ | <i>''Photo from ''</i><br> | ||
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| == What is a mineral ? == | == What is a mineral ? == | ||
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| A mineral ''crystalline structure'' refers to the orderly spatial arrangement of atoms in its molecular structure. There are 14 basic arrangements of atoms in three dimensions, and all mineral structure recognised till now fit in one of these 14 arrangements. | A mineral ''crystalline structure'' refers to the orderly spatial arrangement of atoms in its molecular structure. There are 14 basic arrangements of atoms in three dimensions, and all mineral structure recognised till now fit in one of these 14 arrangements. | ||
| Chemistry and structure define together a mineral. In fact, two or more minerals may have the same chemical composition, but different structures. For example, ] and ] are both iron sulfide. Similarly, some minerals have different chemical compositions, but the same structure : for example, ] (made from silicon and oxygen) and ] (aluminium and phosphorous). |
Chemistry and structure define together a mineral. In fact, two or more minerals may have the same chemical composition, but different structures (these are known as ''polymorphs''). For example, ] and ] are both iron sulfide. Similarly, some minerals have different chemical compositions, but the same structure : for example, ] (made from silicon and oxygen) and ] (aluminium and phosphorous). | ||
| Structure influences greatly a mineral physical properties. For example, though diamond and graphite have the same composition, ] is very soft, while ] is the hardest of all minerals. | Structure influences greatly a mineral physical properties. For example, though diamond and graphite have the same composition, ] is very soft, while ] is the hardest of all minerals. | ||
| To be classified as a true mineral, a substance must be a ] and have a ] structure. Mineral-like substances that don't strictly meet the definition are sometimes classified as ]s. | To be classified as a true mineral, a substance must be a ] and have a ] structure. Mineral-like substances that don't strictly meet the definition are sometimes classified as ]s. | ||
| The study of minerals is called ]. | |||
| ⚫ | ] |
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| ⚫ | ''Photo from '' | ||
| ⚫ | === |
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| Some important rock-forming minerals include the ], ], ], ], ], ], and ]. Other well-known minerals include the wide variety of ]. | |||
| === Minerals and rocks === | === Minerals and rocks === | ||
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| === Physical properties of minerals === | === Physical properties of minerals === | ||
| There are about 3000 different mineral species known, and classifying them 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 |
There are about 3000 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 including some modern techniques such as chemical analysis and ] diffraction, which however, can be costly, time-consuming, and even risk damaging the sample. | ||
| Physical properties commonly used are : | Physical properties commonly used are : | ||
| * |
* '']'': 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). | |||
| * color | |||
| * |
* ''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. | ||
| * |
* '']'' relates the mineral weight to the weight of an equal volume of water. | ||
| * |
* Other properties: ] (response to ultraviolet light), magnetism, radioactivity, tenacity (response to mechanical induced changes of shape or form). | ||
| ⚫ | === Chemical properties of minerals === | ||
| Trying to list all the minerals here would probably be counter-productive; maybe they can be linked from their chemical compositions (eg '']''->], ], ])? | |||
| Minerals may be classified according to their chemical makeup and are listed below in approximate order of their abundance in the Earth's ]. | |||
| ==== Silicates==== | |||
| The largest group of minerals by far are the ]s, which are composed largely of ] and ], with the addition of ]s such as ], ] and ]. Some important rock-forming silicates include the ], ], ], ], ] and ]. | |||
| ==== Carbonates ==== | |||
| The ]s consist of those minerals containing the ] CaCO<sub>3</sub> and include ] (calcium carbonate), ] (magnesium carbonate) and ] (iron carbonate). Carbonates are commonly deposited in marine settings when the shells of dead ] life settle and accumulate on the sea floor. Carbonates are also found in ] regions, where the dissolution and reprecipitation of carbonates leads to the formation of ]s, ]s and ]. | |||
| ==== Sulfates ==== | |||
| ]s all contain the sulfate cation, in the form SO<sub>4</sub>. Sulfates commonly form in ] settings where highly saline waters slowly evaporate, allowing the formation of both sulfates and halides (q.v.) at the water-sediment interface. Common sulfates include ] (calcium sulfate) and ] (hydrated calcium sulfate). | |||
| ==== Halides ==== | |||
| The ]s are the group of minerals forming the natural ]s and include ], common salt (known as ]) and ] (ammonium chloride). Halides, like sulfates, are commonly found in evaporitic settings such as ]s and landlocked seas (e.g. the ]). | |||
| ==== Oxides ==== | |||
| ]s are extremely important in ] 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 ] (iron oxide = rust), ] (magnesium aluminium oxide - a common component of the ]) and ] (hydrogen oxide!). | |||
| ==== Sulfides ==== | |||
| Many ]s are also economically important as metal ores. Common sulfides include ] (copper iron sulfide) and ] (lead sulfide). | |||
| ==== Phosphates ==== | |||
| The ] group actually includes any mineral with a tetrahedral unit AO<sub>4</sub> where A can be ], ], ] or ]. By far the most common phosphate is ] which is an important ] mineral found in teeth and bones of many animals. | |||
| == Dietary mineral == | == Dietary mineral == | ||
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| Sometimes minerals are added to the diet separately from food, as vitamin and mineral supplements and in dirt eating, called pica or ]. | Sometimes minerals are added to the diet separately from food, as vitamin and mineral supplements and in dirt eating, called pica or ]. | ||
| == Selected Minerals == | |||
| *] | |||
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| *], ], ], ], ], ], ], ] | |||
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| == See also == | == See also == | ||
| *] | |||
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| == External links== | == External links== | ||
| *] | |||
Revision as of 09:26, 4 March 2003
Minerals are natural compounds formed through geological processes. The term "mineral" encompasses not only the material's chemical composition but also the crystalline atomic structure. 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.
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Photo from US Geological Survey |
What is a mineral ?
A mineral crystalline structure refers to the orderly spatial arrangement of atoms in its molecular structure. There are 14 basic arrangements of atoms in three dimensions, and all mineral structure recognised till now fit in one of these 14 arrangements.
Chemistry and structure define together a mineral. In fact, two or more minerals may have the same chemical composition, but different structures (these are known as polymorphs). For example, pyrite and marcassite are both iron sulfide. Similarly, some minerals have different chemical compositions, but the same structure : for example, quartz (made from silicon and oxygen) and berlinite (aluminium and phosphorous).
Structure influences greatly a mineral physical properties. For example, though diamond and graphite have the same composition, graphite is very soft, while diamond is the hardest of all minerals.
To be classified as a true mineral, a substance must be a solid and have a crystal structure. Mineral-like substances that don't strictly meet the definition are sometimes classified as mineraloids.
Minerals and rocks
Minerals must be distinguished from rocks. A mineral is a chemical compound with a given composition and a defined atomic structure. A rock is a mixture of one or several minerals, in varying proportions.
Physical properties of minerals
There are about 3000 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 including some modern techniques such as 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 their chemical makeup and are listed below 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 cation CaCO3 and include calcite (calcium carbonate), aragonite (magnesium 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 karst regions, where the dissolution and reprecipitation of carbonates leads to the formation of caves, stalactites and stalagmites.
Sulfates
Sulfates all contain the sulfate cation, in the form SO4. Sulfates commonly form in evaporitic settings where highly saline waters slowly evaporate, allowing the formation of both sulfates and halides (q.v.) at the water-sediment interface. Common sulfates include anhydrite (calcium sulfate) and gypsum (hydrated calcium sulfate).
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 sulfates, 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 = rust), spinel (magnesium aluminium oxide - a common component of the mantle) and ice (hydrogen oxide!).
Sulfides
Many sulfides are also economically important as metal ores. Common sulfides include chalcopyrite (copper iron sulfide) and galena (lead sulfide).
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.
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.