Mineral
From Wikipedia
Mineral atau galian adalah sebatian semulajadi yang dibentuk menerusi proses geologi. Perkataan "mineral" merangkumi bukan hanya komposisi kimia sesuatu bahan tetapi juga struktur mineral. Komposisi mineral berbeza daripada unsur tulen dan garam mudah kepada silikat yang amat kompleks dengan beribu-ribu bentuk yang diketahui (sebatian organik biasanya tidak dikira). Kajian ke atas mineral ini dikenali sebagai mineralogi.
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[Sunting] Takrifan dan pengelasan mineral
Untuk mengklasifikasikan sesuatu itu sebagai mineral yang sebenar, sesuatu bahan itu mesti berada dalam bentuk pepejal dan mempunyai struktur kekristalan.Ia juga mesti juga bukan dari bahan organik,terjadi secara semulajadi,dan mempunyai komposisi kimia yang tersendiri.Komposisi kimia mungkin berbeza-beza dengan mineral-mineral lain.Seperti contoh plagioclase dan feldspar, ia membentuk satu siri berterusan daripada kaya-natrium albite (NaAlSi3O8) hingga kaya-kalsium anorthite (CaAl2Si2O8) dengan empat komposisi pertengahan yang dikenali di tengah-tengah. Bahan-bahan semacam mineral yang tidak mengikut definisi mineral kadangkala diklasifikasikan sebagai mineraloid. Bahan-bahan semulajadu yang wujud adalah bukan mineral. Mineral industri adalah satu bentuk komersial dan merujuk peada bahan-bahan komersial yang bernilai (lihat juga bahagian mineral dan batuan di bawah).
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A crystal structure is the orderly geometric spatial arrangement of atoms in the internal structure of a mineral. There are 14 basic crystal 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 as the mineral form. Even when the mineral grains are too small to see or are irregularly shaped 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 differ in crystal structure (these are known as polymorphs). For example, pyrite and marcasite are both iron sulfide. 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.
Crystal structure greatly influences 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 known 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.
[Sunting] Mineral dan batuan
A mineral is a naturally occurring, inorganic solid with a definite chemical composition and a crystalline structure. A rock is an aggregate of one or more minerals. (A rock may also include organic remains.) The specific minerals in a rock can 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.
Commercially valuable minerals and rocks are referred to as industrial minerals.
[Sunting] Ciri-ciri fizikal mineral
Classifying minerals can range from simple 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 chemical or X-ray diffraction analysis; these methods, however, can be costly, time-consuming, and even risk damaging the sample.
Physical properties commonly used are :
- 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.
- 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).
Metallic -high reflectivity like metal, e.g. galena
Sub-metallic -slightly less than metallic reflectivity, e.g. magnetite
Vitreous -the lustre of a broken glass, e.g. quartz
Pearly -a very soft light shown by some layer silicates, e.g. talc
Silky -a soft light shown by fibrous materials, e.g. gypsum
Dull/earthy -shown by finely crystallised minerals, e.g. the kidney ore variety of hematite
- 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).
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Streak refers to the color of the powder a mineral leaves after rubbing it on an unglazed porcelain streak plate.
- Cleavage describes the way a mineral may come apart or cleave in different ways. 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 acids.
[Sunting] Ciri-ciri kimia mineral
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. The list follows the Dana classification system.
[Sunting] Kelas silikat
The largest group of minerals by far are the 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 feldspars, quartz, olivines, pyroxenes, amphiboles, garnets, and micas.
[Sunting] Kelas karbonat
The carbonate minerals 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. The carbonate class also includes the nitrate and borate minerals.
[Sunting] Kelas sulfat
Sulfates all contain the sulfate anion, in the form SO42-. Sulfates commonly form in 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.
[Sunting] Kelas halida
The halides are the group of minerals forming the natural salts 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 lakes and landlocked seas such as the Dead Sea and Great Salt Lake. The halide class includes the fluoride, chloride, and iodide minerals.
[Sunting] Kelas oksida
Oxides 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. 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.
[Sunting] Kelas sulfida
Many sulfides are economically important as metal ores. Common sulfides include pyrite (iron sulfide - commonly known as fools' gold), chalcopyrite (copper iron sulfide) and galena (lead sulfide). The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, and the sulfosalts (sulfur and a second anion such as arsenic).
[Sunting] Kelas fosfat
The phosphate mineral 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. The phosphate class includes the phosphate, arsenate, vanadate, and antimonate minerals.
[Sunting] Kelas unsur
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).
[Sunting] Lihat juga
- A list of minerals with associated Wikipedia articles
- 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 wool
- Mining
- Norman L. Bowen
- Quarry
- Dietary mineral
[Sunting] Pautan luar
- Mineral gallery
- Minerals.net
- mindat.org mineral database
- Webmineral.com
- a directory of on-line databases related to mineralogy and crystallography
