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Hypersolvus
In hypersolvus granites, as used by Tuttle and Bowen in 1958,TUTTLE O.F. & BOWEN N.L. (1958): Origin of granite in the light of experimental studies in the system NaAlSi3O8-KAlSi3O8-SiO2-H2O, ''Geological Society of America Memoirs'', 74, 153 p crystallization at relatively low water pressures results in the formation of a single feldspar as opposed to subsolvus granites in which two distinct types of feldspar are present. The distinctive character of feldspar in hypersolvus granite is to present exsolution A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The wo ... textures. That is because the high temperature feldspar was ternary (i.e. contained comparable parts of the Ca, Na, K components) and was later dissociated during the cooling phase into K-rich parts and Na-Ca-rich parts, within t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subsolvus
In subsolvus or ''two feldspar'' granites crystallisation occurs at high water pressures resulting in the formation of two types of feldspar as opposed to hypersolvus granites in which crystallization at relatively low water pressures results in the formation of a single feldspar variety. Quoting Tuttle and Bowen in 1958 (abstract, page 3): ″''A classification of salic rocks based on the nature of the alkali feldspar is proposed. The classification has two major divisions: (1) subsolidus, and (2) hypersolvus, depending on the whereabouts of the soda feldspar. In the hypersolvus rocks all the soda feldspar is or was in solid solution in the potash feldspar whereas in the subsolvus rocks the plagioclase is present as discrete grains. The two major divisions are further subdivided according to the nature of the alkali feldspar modification.''″ Note that here the word "subsolidus" unfortunately looks like a misprint and probably has to be replaced by "subsolvus". The two types of fe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Granites
Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies underground. It is common in the continental crust of Earth, where it is found in igneous intrusions. These range in size from dikes only a few centimeters across to batholiths exposed over hundreds of square kilometers. Granite is typical of a larger family of ''granitic rocks'', or '' granitoids'', that are composed mostly of coarse-grained quartz and feldspars in varying proportions. These rocks are classified by the relative percentages of quartz, alkali feldspar, and plagioclase (the QAPF classification), with true granite representing granitic rocks rich in quartz and alkali feldspar. Most granitic rocks also contain mica or amphibole minerals, though a few (known as leucogranites) contain almost no dark minerals. Granite is nearly alwa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feldspar
Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldspars and the ''alkali'' (potassium-sodium) feldspars. Feldspars make up about 60% of the Earth's crust, and 41% of the Earth's continental crust by weight. Feldspars crystalize from magma as both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of calcic plagioclase feldspar is known as anorthosite. Feldspars are also found in many types of sedimentary rocks. Compositions The feldspar group of minerals consists of tectosilicates, silicate minerals in which silicon ions are linked by shared oxygen ions to form a three-dimensional network. Compositions of major elements in common feldspars can be expressed in terms of three endmembers: * potassium feldspar (K- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exsolution
A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word "solution" is used to describe the intimate mixing of components at the atomic level and distinguishes these homogeneous materials from physical mixtures of components. Two terms are mainly associated with solid solutions - ''solvents'' and ''solutes,'' depending on the relative abundance of the atomic species. In general if two compounds are isostructural then a solid solution will exist between the end members (also known as parents). For example sodium chloride and potassium chloride have the same cubic crystal structure so it is possible to make a pure compound with any ratio of sodium to potassium (Na1-xKx)Cl by dissolving that ratio of NaCl and KCl in water and then evaporating the solution. A member of this family is sold under t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ternary Form
Ternary form, sometimes called song form, is a three-part musical form consisting of an opening section (A), a following section (B) and then a repetition of the first section (A). It is usually schematized as A–B–A. Prominent examples include the da capo aria "The trumpet shall sound" from Handel's ''Messiah'', Chopin's Prelude in D-Flat Major "Raindrop", ( Op. 28) and the opening chorus of Bach's '' St John Passion''. Simple ternary form In ternary form each section is self-contained both thematically as well as tonally (that is, each section contains distinct and complete themes), and ends with an authentic cadence. The B section is generally in a contrasting but closely related key, usually a perfect fifth above or the parallel minor of the home key of the A section (V or i); however, in many works of the Classical period, the B section stays in tonic but has contrasting thematic material. It usually also has a contrasting character; for example section A might ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perthite
Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar (near K-feldspar, KAlSi3O8, in composition) includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar (near albite, NaAlSi3O8, in composition). Typically, the host grain is orthoclase or microcline, and the lamellae are albite. If sodic feldspar is the dominant phase, the result is an antiperthite and where the feldspars are in roughly equal proportions the result is a mesoperthite. The intergrowth forms by exsolution due to cooling of a grain of alkali feldspar with a composition intermediate between K-feldspar and albite. There is complete solid solution between albite and K-feldspar at temperatures near 700 °C and pressures like those within the crust of the Earth, but a miscibility gap is present at lower temperatures. If an alkali feldspar grain with an intermediate composition cools slowly enough, K-rich and more Na-rich feldspar domains se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
