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</style><table class="infobox"><tbody><tr><th colspan="2" class="infobox-above" style="color:black; background-color: #8BAFDA">Gedrite</th></tr><tr><td colspan="2" class="infobox-image"><div class="infobox-caption">Gedrite on a <a href="Feldspar" title="Feldspar">feldspar</a> <a href="Matrix_(geology)" title="Matrix (geology)">matrix</a></div></td></tr><tr><th colspan="2" class="infobox-header" style="color:black; background-color: #8BAFDA">General</th></tr><tr><th scope="row" class="infobox-label">Category</th><td class="infobox-data">Inosilicate, ferromagnesian amphibole group</td></tr><tr><th scope="row" class="infobox-label"><a href="Chemical_formula" title="Chemical formula">Formula</a></th><td class="infobox-data"><style data-mw-deduplicate="TemplateStyles:r1123817410">

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</style><span class="chemf nowrap">Mg<sub class="template-chem2-sub">2</sub>(Mg<sub class="template-chem2-sub">3</sub>Al<sub class="template-chem2-sub">2</sub>)(Si<sub class="template-chem2-sub">6</sub>Al<sub class="template-chem2-sub">2</sub>)O<sub class="template-chem2-sub">22</sub>(OH)<sub class="template-chem2-sub">2</sub></span></td></tr><tr><th scope="row" class="infobox-label"><a href="List_of_mineral_symbols" title="List of mineral symbols">IMA symbol</a></th><td class="infobox-data">Ged<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup></td></tr><tr><th scope="row" class="infobox-label"><a href="Nickel%E2%80%93Strunz_classification" title="Nickel–Strunz classification">Strunz classification</a></th><td class="infobox-data">9.DD.05</td></tr><tr><th scope="row" class="infobox-label"><a href="Crystal_system" title="Crystal system">Crystal system</a></th><td class="infobox-data"><a href="Orthorhombic" class="mw-redirect" title="Orthorhombic">Orthorhombic</a></td></tr><tr><th scope="row" class="infobox-label"><a href="Crystal_class" class="mw-redirect" title="Crystal class">Crystal class</a></th><td class="infobox-data">Dipyramidal (mmm) <br><a href="H-M_symbol" class="mw-redirect" title="H-M symbol">H-M symbol</a>: (2/m 2/m 2/m)</td></tr><tr><th scope="row" class="infobox-label"><a href="Space_group" title="Space group">Space group</a></th><td class="infobox-data"><i>Pnma</i></td></tr><tr><th scope="row" class="infobox-label"><a href="Crystal_structure#Unit_cell" title="Crystal structure">Unit cell</a></th><td class="infobox-data">a = 18.59, b = 17.89 <br>c = 5.3 [Å]; Z = 4</td></tr><tr><th colspan="2" class="infobox-header" style="color:black; background-color: #8BAFDA">Identification</th></tr><tr><th scope="row" class="infobox-label">Color</th><td class="infobox-data">White, gray, brown, green, black</td></tr><tr><th scope="row" class="infobox-label"><a href="Crystal_habit" title="Crystal habit">Crystal habit</a></th><td class="infobox-data">Bladed and prismatic crystals; fibrous and sheath like aggregates.</td></tr><tr><th scope="row" class="infobox-label"><a href="Crystal_twinning" title="Crystal twinning">Twinning</a></th><td class="infobox-data">contact twinning</td></tr><tr><th scope="row" class="infobox-label"><a href="Cleavage_(crystal)" title="Cleavage (crystal)">Cleavage</a></th><td class="infobox-data">56 and 126° – good; {210} perfect</td></tr><tr><th scope="row" class="infobox-label"><a href="Fracture_(mineralogy)" title="Fracture (mineralogy)">Fracture</a></th><td class="infobox-data">Splintery</td></tr><tr><th scope="row" class="infobox-label"><a href="Mohs_scale_of_mineral_hardness" class="mw-redirect" title="Mohs scale of mineral hardness">Mohs scale</a> hardness</th><td class="infobox-data">5.5–6</td></tr><tr><th scope="row" class="infobox-label"><a href="Lustre_(mineralogy)" title="Lustre (mineralogy)">Luster</a></th><td class="infobox-data">Vitreous to silky</td></tr><tr><th scope="row" class="infobox-label"><a href="Transparency_and_translucency" title="Transparency and translucency">Diaphaneity</a></th><td class="infobox-data">Translucent, will transmit light on thin edges.</td></tr><tr><th scope="row" class="infobox-label"><a href="Specific_gravity" class="mw-redirect" title="Specific gravity">Specific gravity</a></th><td class="infobox-data">3.18–3.33</td></tr><tr><th scope="row" class="infobox-label">Optical properties</th><td class="infobox-data">Biaxial (+)</td></tr><tr><th scope="row" class="infobox-label"><a href="Refractive_index" title="Refractive index">Refractive index</a></th><td class="infobox-data">n<sub>α</sub> = 1.671 n<sub>β</sub> = 1.681 n<sub>γ</sub> = 1.690</td></tr><tr><th scope="row" class="infobox-label"><a href="Birefringence" title="Birefringence">Birefringence</a></th><td class="infobox-data">δ = 0.019</td></tr><tr><th scope="row" class="infobox-label"><a href="Pleochroism" title="Pleochroism">Pleochroism</a></th><td class="infobox-data">Weak to moderate</td></tr><tr><th scope="row" class="infobox-label"><a href="2V_angle" class="mw-redirect" title="2V angle">2V angle</a></th><td class="infobox-data">Measured: 75°</td></tr><tr><th scope="row" class="infobox-label">References</th><td class="infobox-data"><sup id="cite_ref-Handbook_2-0" class="reference"><a href="#cite_note-Handbook-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Webmin_3-0" class="reference"><a href="#cite_note-Webmin-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup></td></tr></tbody></table>

<p><b>Gedrite</b> is a <a href="Crystalline" class="mw-redirect" title="Crystalline">crystal</a> belonging to the <a href="Crystal_system" title="Crystal system">orthorhombic</a> ferromagnesian subgroup of the <a href="Amphibole" title="Amphibole">amphibole</a> supergroup of the double chain <a href="Classification_of_minerals_-_Silicates" class="mw-redirect" title="Classification of minerals - Silicates">inosilicate</a> minerals with the ideal chemical formula <span class="chemf nowrap">Mg<sub class="template-chem2-sub">2</sub>(Mg<sub class="template-chem2-sub">3</sub>Al<sub class="template-chem2-sub">2</sub>)(Si<sub class="template-chem2-sub">6</sub>Al<sub class="template-chem2-sub">2</sub>)O<sub class="template-chem2-sub">22</sub>(OH)<sub class="template-chem2-sub">2</sub></span>.

</p><p>Gedrite is the <a href="Magnesium" title="Magnesium">magnesium</a> (Mg) rich <a href="Endmember" title="Endmember">endmember</a> of a <a href="Solid_solution" title="Solid solution">solid solution</a> series, with <a href="Divalent" class="mw-redirect" title="Divalent">divalent</a> magnesium <a href="Cation" class="mw-redirect" title="Cation">cations</a> readily replaced with <a href="Ferrous" title="Ferrous">ferrous</a> <a href="Iron" title="Iron">iron</a> (Fe), leading to the iron rich endmember 'ferrogedrite', with the formula: <span class="chemf nowrap">Fe<sup class="template-chem2-sup">2+</sup><sub class="template-chem2-sub">2</sub>(Fe<sup class="template-chem2-sup">2+</sup><sub class="template-chem2-sub">3</sub>Al<sub class="template-chem2-sub">2</sub>)(Si<sub class="template-chem2-sub">6</sub>Al<sub class="template-chem2-sub">2</sub>)O<sub class="template-chem2-sub">22</sub>(OH)<sub class="template-chem2-sub">2</sub></span>. However, pure endmembers are very rare, with often either one of the mentioned cations dominating the composition. Thus, the formula can be written in such a way to express common intermediary gedrite samples:

<span class="chemf nowrap">(Mg,Fe)<sup class="template-chem2-sup">2+</sup><sub class="template-chem2-sub">2</sub>(Mg,Fe)<sup class="template-chem2-sup">2+</sup><sub class="template-chem2-sub">3</sub>Al<sub class="template-chem2-sub">2</sub>(Al<sub class="template-chem2-sub">2</sub>Si<sub class="template-chem2-sub">6</sub>O<sub class="template-chem2-sub">22</sub>)(OH)<sub class="template-chem2-sub">2</sub></span>.

</p><p>Divalent <a href="Manganese" title="Manganese">manganese</a> (Mn) may substitute for some of the magnesium. Trivalent or <a href="Ferric" title="Ferric">ferric</a> iron, or <a href="Titanium" title="Titanium">titanium</a><sup>4+</sup> may replace some of the <a href="Aluminum" class="mw-redirect" title="Aluminum">aluminum</a> (Al). <a href="Fluorine" title="Fluorine">Fluorine</a> and <a href="Chlorine" title="Chlorine">chlorine</a> are common substitutes for the <a href="Hydroxyl" class="mw-redirect" title="Hydroxyl">hydroxyl</a> (OH) in amphoboles. Other chemical impurities may include <a href="Calcium" title="Calcium">calcium</a>, <a href="Sodium" title="Sodium">sodium</a>, and <a href="Potassium" title="Potassium">potassium</a>.

</p><p>Gedrite also forms a series with another ferromagnesian amphibole, <a href="Anthophyllite" title="Anthophyllite">anthophyllite</a>.

</p><p>Gedrite occurs in <a href="Contact_metamorphism" class="mw-redirect" title="Contact metamorphism">contact</a> and medium to high grade <a href="Metamorphic_rock" title="Metamorphic rock">metamorphic rocks</a> in association with <a href="Garnet" title="Garnet">garnet</a>, <a href="Cordierite" title="Cordierite">cordierite</a>, <a href="Anthophyllite" title="Anthophyllite">anthophyllite</a>, <a href="Cummingtonite" title="Cummingtonite">cummingtonite</a>, <a href="Sapphirine" title="Sapphirine">sapphirine</a>, <a href="Sillimanite" title="Sillimanite">sillimanite</a>, <a href="Kyanite" title="Kyanite">kyanite</a>, <a href="Quartz" title="Quartz">quartz</a>, <a href="Staurolite" title="Staurolite">staurolite</a> and <a href="Biotite" title="Biotite">biotite</a>.<sup id="cite_ref-Handbook_2-1" class="reference"><a href="#cite_note-Handbook-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

</p><p>Gedrite was first described for an occurrence in <a href="G%C3%A8dre" title="Gèdre">Gèdre</a>, <a href="Hautes-Pyr%C3%A9n%C3%A9es" title="Hautes-Pyrénées">Hautes-Pyrénées</a>, France in 1836.<sup id="cite_ref-Webmin_3-1" class="reference"><a href="#cite_note-Webmin-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="CITEREFWarr2021" class="citation journal cs1">Warr, L.N. (2021). <a rel="nofollow" class="external text" href="https://doi.org/10.1180%2Fmgm.2021.43">"IMA–CNMNC approved mineral symbols"</a>. <i>Mineralogical Magazine</i>. <b>85</b> (3): <span class="nowrap">291–</span>320. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2021MinM...85..291W">2021MinM...85..291W</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1180%2Fmgm.2021.43">10.1180/mgm.2021.43</a></span>. <a href="S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:235729616">235729616</a>.</cite></span>

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<li id="cite_note-Handbook-2"><span class="mw-cite-backlink">^ <a href="#cite_ref-Handbook_2-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Handbook_2-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a rel="nofollow" class="external free" href="http://www.handbookofmineralogy.org/pdfs/gedrite.pdf">http://www.handbookofmineralogy.org/pdfs/gedrite.pdf</a> Handbook of Mineralogy</span>

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<li id="cite_note-Webmin-3"><span class="mw-cite-backlink">^ <a href="#cite_ref-Webmin_3-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Webmin_3-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a rel="nofollow" class="external free" href="http://webmineral.com/data/Gedrite.shtml">http://webmineral.com/data/Gedrite.shtml</a> Webmineral</span>

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<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external free" href="http://www.mindat.org/min-1665.html">http://www.mindat.org/min-1665.html</a> Mindat</span>

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<li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://pubsites.uws.edu.au/ima-cnmnc/">IMA Master List</a></span>

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