| 词条 | Andalusite |
| 释义 |
| name = Andalusite | category = Nesosilicates | image = AndalousiteTyrol.jpg | imagesize = 260px | alt = | caption = Andalusite, Tyrol Austria. | formula = Al2SiO5 | molweight = | strunz = 9.AF.10 | system = Orthorhombic | class = Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) | symmetry = Pnnm | unit cell = a = 7.7980 Å, b = 7.9031 Å c = 5.5566 Å; Z = 4 | color = Pink, violet, yellow, green, white, gray; in thin section, colorless to pink or green | habit = As euhedral crystals or columnar aggregates having nearly square cross sections; fibrous compact to massive | twinning = On {101}, rare | cleavage = Good on {110}, poor on {100} | fracture = uneven to subconchoidal | mohs = 6.5 - 7.5 | luster = Vitreous | polish = | refractive = nα = 1.629 - 1.640 nβ = 1.633 - 1.644 nγ = 1.638 - 1.650 | opticalprop = double refractive, biaxial negative; chiastolite has anomalous aggregate reaction.[1] | birefringence = δ = 0.009 - 0.010 | dispersion = r < v strong | pleochroism = strongly trichroic | 2V = 71 - 86° | fluorescence= non-fluorescent | absorption = | streak = White | gravity = 3.17 (+/- .04) | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent to nearly opaque with inclusions | other = | references = [1][2] }} Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5. This mineral was called andalousite by Delamétehrie[3], who thought it came from Andalusia. It soon became clear that it was a locality error, and that the specimens studied were actually from El Cardoso de la Sierra, in the province of Guadalajara, not Andalusia.[4] However, the error remains in many books. Andalusite is trimorphic with kyanite and sillimanite, being the lower pressure mid temperature polymorph. At higher temperatures and pressures, andalusite may convert to sillimanite. Thus, as with its other polymorphs, andalusite is an aluminosilicate index mineral, providing clues to depth and pressures involved in producing the host rock.[5] {{al2sio5 phase diagram}}VarietiesThe variety chiastolite commonly contains dark inclusions of carbon or clay which form a cruciform pattern when shown in cross-section. This stone was known at least from the sixteenth century, being taken to many European countries, as a souvenir, by pilgrims returning from Santiago de Compostela.[6] A clear variety found in Brazil and Sri-Lanka can be cut into a gemstone.[7] Faceted andalusite stones give a play of red, green, and yellow colors that resembles a muted form of iridescence, although the colors are actually the result of unusually strong pleochroism. It is associated with mica schist which increases alkali content in ultimate product and so it has not been exploited economically so far. Andalusite is an aluminium compound with high heat resistance used in furnaces, kilns and other industrial processes. South Africa possesses by far the largest portion of the world's known andalusite deposits. OccurrenceAndalusite is a common metamorphic mineral which forms under low pressure and low to high temperatures. The minerals kyanite and sillimanite are polymorphs of andalusite, each occurring under different temperature-pressure regimes and are therefore rarely found together in the same rock. Because of this the three minerals are a useful tool to help identify the pressure-temperature paths of the host rock in which they are found. An example rock includes hornfels. See also{{commonscat|Andalusite}}
References1. ^1 Gemological Institute of America, GIA Gem Reference Guide 1995, {{ISBN|0-87311-019-6}} 2. ^http://rruff.geo.arizona.edu/doclib/hom/andalusite.pdf Handbook of Mineralogy 3. ^{{Cite journal|last=Delamétherie|first=Jean Claude|date=1798|title=Sur une pierre de l’Andalousie|url=|journal=Journal de Physique, de Chimie d’Histoire Naturelle et des Arts|volume=46|pages=386-387|via=}} 4. ^{{Cite book|title=Minerales y Minas de España. Vol. IX. Silicatos|last=Calvo|first=Miguel|publisher=Escuela Técnica Superior de Ingenieros de Minas de Madrid. Fundación Gómez Pardo|year=2018|isbn=978-84-8321-883-9|location=Madrid, Spain|pages=91-94}} 5. ^{{Cite journal|last=Whitney, D.L.|first=|date=2002|title="Coexisting andalusite, kyanite, and sillimanite: Sequential formation of three Al2SiO5 polymorphs during progressive metamorphism near the triple point, Sivrihisar, Turkey|url=|journal=American Mineralogist|volume=87|pages=405-416|via=}} 6. ^{{Cite journal|last=Calvo|first=Miguel|date=2016|title=El “lapis crucifer”, “piedra de cruz de Compostela”: un elemento importante de los patrimonios geológico y cultural del NW de España|url=|journal=De Re Metallica|volume=6|pages=67-79|via=}} 7. ^{{Cite web |url=http://www.gemstone.org/gem-by-gem/english/andalusite.html |title=International Colored Gem Association: Anadalusite |access-date=2006-07-13 |archive-url=https://web.archive.org/web/20060717224731/http://www.gemstone.org/gem-by-gem/english/andalusite.html |archive-date=2006-07-17 |dead-url=yes |df= }} 4 : Aluminium minerals|Nesosilicates|Orthorhombic minerals|Industrial minerals |
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