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Demantoid
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{{Short description|Green gemstone variety of the mineral andradite}} {{distinguish|Demonoid|Diamondoid}} {{Infobox mineral | name = Demantoid | category = | boxwidth = | boxbgcolor = | image = Andradite-Stilbite-Ca-dem05a.jpg | imagesize = 260px | caption = Demantoid with [[stilbite]] | formula = Ca<sub>3</sub>Fe<sub>2</sub>Si<sub>3</sub>O<sub>12</sub> | molweight = | color = light to deep green | habit = | system = cubic | twinning = | cleavage = | fracture = | mohs = 6.5β7.0 | luster = adamantine | polish = | refractive = 1.880β1.889<ref name="ICA">{{cite web|author=Idar-Oberstein|url=http://www.gemstone.org/gem-by-gem/english/demantoid.html|title=Demantoid|publisher=International Colored Gemstone Association|accessdate=January 25, 2007|url-status=dead|archiveurl=https://web.archive.org/web/20080624171321/http://www.gemstone.org/gem-by-gem/english/demantoid.html|archivedate=June 24, 2008}}</ref> | opticalprop = Single Refractive | birefringence = | dispersion = 0.057 | pleochroism = none | fluorescence= | absorption = | streak = | gravity = 3.84 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = | impurities = Cr | other = }} [[File:Granat demantoid - Antetezambato, Ambanja District, Diana (Northern) Region, Antsiranana Province, Madagaskar.jpg|thumb|Garnet demantoid - Antetezambato, Ambanja District, Diana (Northern) Region, Antsiranana Province, Madagaskar.]] '''Demantoid''' is the green [[gemstone]] variety of the mineral [[andradite]], a member of the [[garnet]] group of [[mineral]]s. Andradite is a [[calcium]]- and [[iron]]-rich garnet. The chemical formula is Ca<sub>3</sub>Fe<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub> with [[chromium]] substitution as the cause of the demantoid green color. Ferric iron is the cause of the yellow in the stone. It has the [[misnomer]]s ''olivine''<ref>{{cite encyclopedia|author=Shipley, Robert M.|encyclopedia=Dictionary of Gems and Gemology|edition=5th|year=1951|publisher=[[Gemological Institute of America]]|pages=62β63|title=Olivine}}</ref> and ''Uralian emerald''. In approximately 2003, reports began to circulate in the trade that some Russian demantoid garnets were being routinely subjected to heat treatment in order to enhance their color. Such treatment is believed to be performed at relatively low temperatures and is thought not to be detectable by [[gemology|gemological]] testing.<ref>Wording in {{cite web|url=http://www.atggems.com/certs/cert_demantoid_202pt_cush_GIA.pdf|title=grading report|publisher=Gemological Institute of America|date=July 2012}}</ref><ref>http://www.gia.edu/research-resources/gems-gemology/issues/winter2012-contents/WN12AB.pdf{{dead link|date=June 2016}}</ref>
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