Editing Epidote

{{Short description|Sorosilicate mineral}}
{{Update-EB|date=November 2019}}
{{Infobox mineral
| name        = Epidote
| category    = [[Silicate mineral#Sorosilicates|Sorosilicates]]
| boxwidth    = 
| boxbgcolor  = #79941d
| boxtextcolor = white
| image       = Эпидот(пушкинит).jpg
| imagesize   = 290px
| caption     =
| formula     = {Ca<sub>2</sub>}{Al<sub>2</sub>Fe<sup>3+</sup>}(SiO<sub>4</sub>)(Si<sub>2</sub>O<sub>7</sub>)O(OH)
| IMAsymbol   = Ep<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| molweight   = 
| system      = [[monoclinic crystal system|Monoclinic]]
| class       = Prismatic (2/m) <br/><small>(same [[Hermann–Mauguin notation|H–M symbol]])</small>
| symmetry    = ''P''2<sub>1</sub>/m
| color       = [[shades of chartreuse|Pistachio green]], [[chartreuse (color)|yellow-green]], greenish black, brownish-green, green, black
| habit       = Prismatic with [[striation (geology)|striations]], fibrous, massive
| twinning    = On [100]
| cleavage    = {001} perfect and {100} imperfect
| fracture    = Flat regular to uneven
| mohs        = 6–7 
| luster      = Vitreous to resinous 
| refractive  = n<sub>α</sub> = 1.715–1.751<br> n<sub>β</sub> = 1.725–1.784<br> n<sub>γ</sub> = 1.734–1.797
| opticalprop = Biaxial (-)
| birefringence = δ = 0.019–0.046
| pleochroism = Strong
| streak      = Greyish white
| gravity     = 3.38–3.49
| density     = 
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| diaphaneity = Transparent to nearly opaque
| other       = 
| references  = <ref>[http://rruff.geo.arizona.edu/doclib/hom/epidote.pdf Epidote]. ''Handbook of Mineralogy''</ref><ref>[http://www.mindat.org/min-1389.html Epidote]. Mindat</ref><ref>[http://webmineral.com/data/Epidote.shtml Epidote]. Webmineral</ref>
}}

'''Epidote''' is a [[calcium]] [[aluminium]] [[iron]] [[Silicate mineral#Sorosilicates|sorosilicate]] [[mineral]].

==Description==
Well developed crystals of epidote, Ca<sub>2</sub>Al<sub>2</sub>(Fe<sup>3+</sup>;Al)(SiO<sub>4</sub>)(Si<sub>2</sub>O<sub>7</sub>)O(OH), [[crystal]]lizing in the [[monoclinic]] system, are of frequent occurrence: they are commonly prismatic in habit, the direction of elongation being perpendicular to the single plane of symmetry. The name Epidote is derived from the Greek word 'epidosis', meaning "increase", in allusion to the crystal characteristic of one longer side at the base of the prism.<ref>{{Cite web |title=About Epidote |url=https://www.mindat.org/min-1389.html}}</ref> The faces are often deeply striated and crystals are often twinned. Many of the characters of the mineral vary with the amount of iron present for instance, the color, the optical constants, and the specific gravity.  The color is green, grey, brown or nearly black, but usually a characteristic shade of yellowish-green or pistachio-green. It displays strong [[pleochroism]], the pleochroic colors being usually green, yellow and brown. [[Clinozoisite]] is green, white or pale rose-red group species containing very little iron, thus having the same chemical composition as the [[orthorhombic]] mineral [[zoisite]].<ref name="EB1911">{{EB1911|inline=y|wstitle=Epidote|volume=9|page=689|first=Leonard James|last=Spencer|author-link=Leonard James Spencer}}</ref> The name, due to [[René Just Haüy|Haüy]], is derived from the Greek word "epidosis" (ἐπίδοσις) which means "addition" in allusion to one side of the ideal prism being longer than the other.

Epidote is an abundant rock-forming mineral, but one of secondary origin. It occurs in [[marble]] and [[schist]]ose rocks of [[metamorphic rock|metamorphic]] origin. It is also a product of [[hydrothermal alteration]] of various minerals ([[feldspar]]s, [[mica]]s, [[pyroxene]]s, [[amphibole]]s, [[garnet]]s, and others) composing [[igneous rocks]]. A rock composed of [[quartz]] and epidote is known as [[epidosite]]. Well-developed crystals are found at many localities: Knappenwand, near the [[Großvenediger]] in the Untersulzbachthal in [[Salzburg]], as magnificent, dark green crystals of long prismatic habit in cavities in epidote schist, with [[asbestos]], [[adularia]], [[calcite]], and [[apatite]]; the Ala valley and [[Traversella]] in [[Piedmont]]; Arendal in [[Norway]]; [[Le Bourg-d'Oisans]] in [[Dauphiné]]; [[Haddam, Connecticut|Haddam]] in [[Connecticut]]; [[Prince of Wales Island (Alaska)|Prince of Wales Island]] in [[Alaska]], here as large, dark green, tabular crystals with [[copper]] [[ore]]s in metamorphosed limestone.<ref name="EB1911"/>

The perfectly transparent, dark green crystals from the Knappenwand and from [[Brazil]] have occasionally been cut as [[gemstone]]s.<ref name="EB1911"/> The green part of several mixed-rock ornamental stones is composed of epidote. These include Unakite and Australian Dragon Bloodstone.

===Related species===
Belonging to the same isomorphous group with epidote are the [[Rare-earth element|REE-rich]] [[allanite]] (containing primarily [[lanthanum]], [[cerium]], and [[yttrium]]), and the [[manganese]]-rich [[piemontite]].

Piemontite occurs as small, reddish-black, monoclinic crystals in the manganese mines at San Marcel, near [[Ivrea]] in Piedmont, and in crystalline schists at several places in [[Japan]]. The purple color of the [[Egypt]]ian porfido rosso antico is due to the presence of this mineral.<ref name="EB1911"/>

Allanite and [[dollaseite-(Ce)]] have the same general epidote formula and contain metals of the cerium group. In external appearance allanite differs widely from epidote, being black or dark brown in color, pitchy in lustre, and opaque in the mass; further, there is little or no cleavage, and well-developed crystals are rare. The crystallographic and optical characters are similar to those of epidote; the pleochroism is strong with reddish-, yellowish-, and greenish-brown colors. Although not a common mineral, allanite is of fairly wide distribution as a primary accessory constituent of many crystalline rocks, [[gneiss]], [[granite]], [[syenite]], [[rhyolite]], [[andesite]], and others. It was first found in the granite of east [[Greenland]] and described by [[Thomas Allan (mineralogist)|Thomas Allan]] in 1808, after whom the species was named. Allanite is a mineral readily altered by hydration, becoming optically isotropic and [[amorphous]]: for this reason several varieties have been distinguished, and many different names applied. Orthite was the name given by [[Jöns Berzelius]] in 1818 to a hydrated form found as slender prismatic crystals, sometimes a foot in length, at Finbo, near [[Falun]] in [[Sweden]].<ref name="EB1911"/> Dollaseite is less common, famous from the Ostanmossa mine in the [[Norberg]] district of [[Sweden]].

==Gallery==

<gallery mode=packed>
Epidotic vesicular basalt (Portage Lake Volcanic Series, upper Mesoproterozoic, 1.093 to 1.097 Ga; Gratiot Mine, Keweenaw Peninsula, Upper Peninsula of Michigan, USA) 3 (9393657643).jpg|Vesicular [[basalt]] with epidote crystal filling
Deformed epidote lens in amphibole epidote schist.jpg|Deformed epidote within [[greenschist]] rock from [[Itogon]], Philippines
Amygdaloidal basalt (Portage Lake Volcanic Series, upper Mesoproterozoic, 1.093 to 1.097 Ga; Keweenaw Peninsula, Upper Peninsula of Michigan, USA) 13.jpg|Amygdaloidal basalt filled with epidote
Epidote-lined vug in basalt (Portage Lake Volcanic Series, upper Mesoproterozoic, 1.093 to 1.097 Ga; Centennial Mine, Keweenaw Peninsula, Upper Peninsula of Michigan, USA) 2.jpg|[[Vug]] in basalt lined with epidote
ÉpidoteFrance Ref374 MuséumHistoireNaturelleLille GLAM2016 Photo.F.Lamiot 19.jpg|Epidote from [[France]]
Epidote crystals.jpg|Epidote from [[Russia]]
Epidot - Haidarabad, Dolina Shigar, Skardu, Pakistan.jpg|Epidote from [[Pakistan]]
Epidote - Canta, Lima, Peru.jpg|Epidote from [[Lima]], [[Peru]]
Epidot DSC 5229.jpg|Epidote from [[Germany]]
ÉpidoteFrance Ref374 MuséumHistoireNaturelleLille GLAM2016 Photo.F.Lamiot 5.jpg|Epidote from France
</gallery>

==References==
{{Reflist}}

==External links==
{{Commons category|Epidote}}
* [https://web.archive.org/web/20040603093346/http://mineral.galleries.com/minerals/silicate/epidote/epidote.htm The mineral Epidote Mineral Galleries]

{{Authority control}}

[[Category:Calcium minerals]]
[[Category:Aluminium minerals]]
[[Category:Iron(III) minerals]]
[[Category:Sorosilicates]]
[[Category:Epidote group]]
[[Category:Monoclinic minerals]]
[[Category:Minerals in space group 11]]