Glaucophane

Glaucophane

Glaucophane is a mineral belonging to the amphibole group, chemical formula Na2(Mg,Fe)3Al2Si8O22(OH)2. It is named from its typical blue color (in Greek, "glaucophane" means "blue appearing"). Glaucophane crystallizes in the monoclinic system.

The blue color is very diagnostic for this species. It, along with the closely related mineral riebeckite are the only common amphibole minerals that are typically blue. Glaucophane forms a solid solution series with ferroglaucophane; Na2(Fe,Mg)3Al2Si8O22(OH)2. Glaucophane is the magnesium-rich member and ferroglaucophane is the iron-rich member. Ferroglaucophane is similar to glaucophane but is denser, generally darker in color with a diminished pearly luster. Glaucophane's hardness is 5 - 6, and its specific gravity is approximately 3 - 3.2.

Glaucophane forms in metamorphic rocks that are either particularly rich in sodium or that have experienced low temperature-high pressure metamorphism such as would occur along a subduction zone. This material has undergone intense pressure and moderate heat as it was subducted downward toward the mantle. It is glaucophane's color that gives the blueschist facies its name. Glaucophane is also found in eclogites that have undergone retrograde metamorphism.

There is also a rare amphibole called holmquistite, chemical formula Li2Mg3Al2Si8O22(OH)2, which occurs only in lithium-rich continental rocks. For many years, holmquistite was mistaken for glaucophane, as the two look identical in thin section.

See also

* List of Minerals


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Look at other dictionaries:

  • Glaucophane — Glaucophane[1] Catégorie IX : silicates[2] …   Wikipédia en Français

  • Glaucophane — Glau co*phane, n. [Gr. glayko s silvery, gray + fai nesqai to appear.] (Min.) A mineral of a dark bluish color, related to amphibole. It is characteristic of certain crystalline rocks. [1913 Webster] …   The Collaborative International Dictionary of English

  • glaucophane — ● glaucophane nom féminin Silicate naturel d aluminium, de fer, de magnésium et de sodium, du groupe des amphiboles, que l on trouve dans les roches métamorphiques de haute pression …   Encyclopédie Universelle

  • glaucophane — /glaw keuh fayn /, n. a sodium rich monoclinic mineral of the amphibole family, usually metamorphic. [1840 50; GLAUCO + PHANE] * * * ▪ mineral       common amphibole mineral, a sodium, magnesium, and aluminum silicate that occurs only in… …   Universalium

  • glaucophane schist facies — One of the major divisions of the mineral facies classification of metamorphic rocks, encompassing rocks whose peculiar mineralogy suggests that they formed under conditions of high pressure and relatively low temperature (generally less than… …   Universalium

  • glaucophane facies — ▪ geology       one of the major divisions of the mineral facies classification of metamorphic rocks, the rocks of which, because of their peculiar mineralogy, suggest formation conditions of high pressure and relatively low temperature; such… …   Universalium

  • glaucophane — noun A mixed aluminate of sodium, magnesium and aluminium that has a characteristic blue colour, and exhibits pleochroism, with the chemical formula Na(Mg,Fe)AlSiO(OH) …   Wiktionary

  • glaucophane — glau·co·phane …   English syllables

  • glaucophane — ˈglȯkəˌfān noun ( s) Etymology: German glaukophan, from glauk glauc + phan phane : a mineral Na2(Mg,Fe)3Al2Si8O22(OH)2 consisting of a blue, bluish black, or grayish silicate of sodium, aluminum, iron, and magnesium occurring in certain… …   Useful english dictionary

  • metamorphic rock — Any of a class of rocks that result from the alteration of preexisting rocks in response to changing geological conditions, including variations in temperature, pressure, and mechanical stress. The preexisting rocks may be igneous, sedimentary,… …   Universalium

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