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Epidote

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Green Monster Mountain, Prince of Wales Island, Prince of Wales-Outer Ketchikan Borough, Alaska, USA
© 2001 John H. Betts

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Formula:
{Ca
 
2
}{Al
 
2
Fe
3+
 
}[O|OH|SiO
 
4
|Si
 
2
O
 
7
]
System:MonoclinicColour:Yellowish-green, green, ...
Lustre:Vitreous, PearlyHardness:6
Name:From the Greek "Epidosis" = "increase" in allusion to the crystal characteristic of one longer side at the base of the prism.


Epidote Group. Clinozoisite-Epidote Series. The Al2Fe³+ analogue of Clinozoisite.

Classification of Epidote

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:8/C.23-20
Nickel-Strunz 10th (pending) edition ID:9.BG.05

9 : SILICATES (Germanates)
B : Sorosilicates
G : Sorosilicates with mixed SiO4 and Si2O7 groups; cations in octahedral [6] and greater coordination
Dana 8th edition ID:58.2.1a.7

58 : SOROSILICATES Insular, Mixed, Single, and Larger Tetrahedral Groups
2 : Insular, Mixed, Single, and Larger Tetrahedral Groups with cations in [6] and higher coordination; single and double groups (n = 1, 2)
Hey's CIM Ref.:16.21.2

16 : Silicates Containing Aluminum and other Metals
21 : Aluminosilicates of Fe and Ca
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Type Occurrence of Epidote

Type Locality:Bourg d'Oisans, Isère, Rhône-Alpes, France
Year of Discovery:1801

Occurrences of Epidote

Geological Setting:Regional and contact metamorphic rocks. Saussuritization (alteration of plagioclase)

Physical Properties of Epidote

Lustre:Vitreous, Pearly
Diaphaneity (Transparency):Transparent, Opaque
Colour:Yellowish-green, green, brownish-green, black
Streak:Colorless
Hardness (Mohs):6
Tenacity:Brittle
Cleavage:Perfect
Perfect on {001}, imperfect on {100}
Fracture:Irregular/Uneven
Density (measured):3.38 - 3.49 g/cm3
Density (calculated):3.43(3) g/cm3

Crystallography of Epidote

Crystal System:Monoclinic
Class (H-M):2/m - Prismatic
Space Group:P21/m (P1 1 21/m) [P21/m] {P1 21/m 1}
Cell Parameters:a = 8.8877(14) Å, b = 5.6275(8) Å, c = 10.1517(12) Å
β = 115.383(14)°
Ratio:a:b:c = 1.579 : 1 : 1.804
Unit Cell Volume:V 458.73 ų (Calculated from Unit Cell)
Z:2
Morphology:Crystals prismatic to 35cm. Fibrous, coarse to fine granular, massive.
Twinning:On {100}, contact, lamellar, common.
Crystal Atlas:
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Epidote no.9 - Goldschmidt (1913-1926)
Epidote no.94 - Goldschmidt (1913-1926)

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Structure
  Reference
Gabe E J Portheine J C Whitlow S H (1973) A reinvestigation of the epidote structure: Confirmation of the iron location sample LEP. American Mineralogist 58:218-223.

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More Crystal Structures
Click here to view more crystal structures at the American Mineralogist Crystal Structure Database
X-Ray Powder Diffraction:
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Radiation - Copper Kα
Data Set:
Horizontal Axis: ° to ° Vertical Axis: % Source Data: Filtered Data: Peaks:
Data courtesy of RRUFF project at University of Arizona, used with permission.

Optical Data of Epidote

Type:Biaxial (-)
RI values: nα = 1.715 - 1.751 nβ = 1.725 - 1.784 nγ = 1.734 - 1.797
2V:Measured: 90° to 116°, Calculated: 62° to 84°
Maximum Birefringence:δ = 0.019 - 0.046

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:High
Dispersion:strong r > v
Pleochroism:Strong
Comments:X= colorless, pale yellow, pale green
Y= greenish yellow
Z= yellowish green

Chemical Properties of Epidote

Formula:
{Ca
 
2
}{Al
 
2
Fe
3+
 
}[O|OH|SiO
 
4
|Si
 
2
O
 
7
]
Essential elements:Al, Ca, H, O, Si
All elements listed in formula:Al, Ca, Fe, H, O, Si
Common Impurities:Al,Mg,Mn

Relationship of Epidote to other Species

Series:Forms a series with Clinozoisite (see here)
Related to:
  • Epidote Group
    • Related Minerals - Nickel-Strunz Grouping):
    9.BG.05Allanite-(Ce)
    {CaCe}{Al
     
    2
    		Fe
    2+
     
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Allanite-(La)
    {CaLa}{Al
     
    2
    		Fe
    2+
     
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Allanite-(Y)
    {CaY}{Al
     
    2
    		Fe
    2+
     
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Clinozoisite
    {Ca
     
    2
    		}{Al
     
    3
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Dissakisite-(Ce)
    {CaCe}{Al
     
    2
    		Mg}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Dollaseite-(Ce)
    {CaCe}{MgAlMg}[F|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Epidote-(Pb)
    {CaPb}{Al
     
    3
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Khristovite-(Ce)
    {CaCe}{MgAlMn
    2+
     
    		}[F|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Mukhinite
    {Ca
     
    2
    		}{Al
     
    2
    		V
    3+
     
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Piemontite
    {Ca
     
    2
    		}{Al
     
    2
    		Mn
    3+
     
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Piemontite-(Sr)
    {CaSr}{Al
     
    2
    		Mn
    3+
     
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Manganiandrosite-(La)
    {LaMn
    2+
     
    		}{Mn
    3+
     
    		AlMn
    2+
     
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Tawmawite
    Ca
     
    2
    		(Al,Fe
    3+
     
    		,Cr)
     
    3
    		[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Manganipiemontite-(Sr)
    {CaSr}{Mn
    3+
     
    		AlMn
    3+
     
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Ferriallanite-(Ce)
    {CaCe}{Fe
    3+
     
    		AlFe
    2+
     
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Clinozoisite-(Sr)
    CaSrAl
     
    3
    		(Si
     
    2
    		O
     
    7
    		)(SiO
     
    4
    		)O(OH)
    9.BG.05Ferriepidote
    9.BG.05Manganiandrosite-(Ce)
    (Mn
    2+
     
    		,Ca)(Ce,REE)AlMn
    3+
     
    		Mn
    2+
     
    		(Si
     
    2
    		O
     
    7
    		)(SiO
     
    4
    		)O(OH)
    9.BG.05Dissakisite-(La)
    {CaLa}{Al
     
    2
    		Mg}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Vanadoandrosite-(Ce)
    {Mn
    2+
     
    		Ce}{V
    3+
     
    		AlMn
    2+
     
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05Androsite-(La)
    9.BG.05Uedaite-(Ce)
    {Mn
    2+
     
    		Ce}{Al
     
    2
    		Fe
    2+
     
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.05IMA2006-055
    CaSrAl
     
    2
    		Fe
    3+
     
    		(Si
     
    2
    		O
     
    7
    		)(SiO
     
    4
    		)O(OH)
    9.BG.10Zoisite
    {Ca
     
    2
    		}{Al
     
    3
    		}[O|OH|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.15Macfallite
    Ca
     
    2
    		(Mn
    3+
     
    		,Al)
     
    3
    		[(OH)
     
    3
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.15Sursassite
    Mn
     
    2
    		Al
     
    3
    		[(OH)
     
    3
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.20Julgoldite-(Fe2+)
    Ca
     
    2
    		(Fe
    2+
     
    		,Mg)(Fe
    3+
     
    		,Al)
     
    2
    		[(OH)
     
    2
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		] · H
     
    2
    		O
    9.BG.20Okhotskite
    Ca
     
    8
    		(Mn,Mg)
     
    4
    		(Mn,Al,Fe)
     
    8
    		Si
     
    12
    		O
     
    56-n
    		(OH)
     
    n
    9.BG.20Pumpellyite-(Fe2+)
    Ca
     
    2
    		Fe
    2+
     
    		Al
     
    2
    		[(OH)
     
    2
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		] · H
     
    2
    		O
    9.BG.20Pumpellyite-(Fe3+)
    Ca
     
    2
    		(Fe
    3+
     
    		,Mg,Fe
    2+
     
    		)(Al,Fe
    3+
     
    		)
     
    2
    		[(OH,O)
     
    2
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		] · H
     
    2
    		O
    9.BG.20Pumpellyite-(Mg)
    Ca
     
    2
    		MgAl
     
    2
    		[(OH)
     
    2
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		] · H
     
    2
    		O
    9.BG.20Pumpellyite-(Mn2+)
    Ca
     
    2
    		(Mn
    2+
     
    		,Mg)(Al,Mn
    3+
     
    		,Fe
    3+
     
    		)
     
    2
    		[(OH)
     
    2
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		] · H
     
    2
    		O
    9.BG.20Shuiskite
    Ca
     
    2
    		(Mg,Al)(Cr,Al)
     
    2
    		[(OH)
     
    2
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		] · 2H
     
    2
    		O
    9.BG.20Julgoldite-(Fe3+)
    Ca
     
    2
    		(Fe
    3+
     
    		,Mg)(Fe
    3+
     
    		,Al)
     
    2
    		[(OH,O)
     
    2
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		] · H
     
    2
    		O
    9.BG.20Pumpellyite-(Al)
    Ca
     
    2
    		(Al,Fe
    2+
     
    		,Mg)Al
     
    2
    		[(OH,O)
     
    2
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		] · H
     
    2
    		O
    9.BG.20Poppiite
    Ca
     
    2
    		(V
    3+
     
    		,Fe
    3+
     
    		,Mg)(V
    3+
     
    		,Al)
     
    2
    		[(OH,O)
     
    2
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		] · H
     
    2
    		O
    9.BG.20Julgoldite-(Mg)
    Ca
     
    2
    		(Mg,Fe
    2+
     
    		)(Fe
    3+
     
    		,Al)
     
    2
    		[(OH)
     
    2
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		] · H
     
    2
    		O
    9.BG.25Ganomalite
    Pb
     
    9
    		Ca
     
    5
    		Mn[O|SiO
     
    4
    		|(Si
     
    2
    		O
     
    7
    		)
     
    4
    		]
    9.BG.30Rustumite
    Ca
     
    10
    		(Si
     
    2
    		O
     
    7
    		)
     
    2
    		(SiO
     
    4
    		)Cl
     
    2
    		(OH)
     
    2
    9.BG.35Vesuvianite
    Ca
     
    10
    		(Mg,Fe)
     
    2
    		Al
     
    4
    		Si
     
    9
    		O
     
    34
    		(OH)
     
    4
    9.BG.35Wiluite
    Ca
     
    19
    		(Al,Mg,Fe,Ti)
     
    13
    		(B,Al,[ ])
     
    5
    		Si
     
    18
    		O
     
    68
    		(O,OH)
     
    10
    9.BG.35Manganvesuvianite
    Ca
     
    19
    		Mn(Al,Mn,Fe)
     
    19
    		(Mg,Mn)
     
    2
    		Si
     
    18
    		O
     
    69
    		(OH)
     
    9
    9.BG.35Fluorvesuvianite
    Ca
     
    19
    		(Al,Mg,Fe
    2+
     
    		)
     
    13
    		[(F,OH,O)
     
    10
    		|(SiO
     
    4
    		)
     
    10
    		|(Si
     
    2
    		O
     
    7
    		)
     
    4
    		]
    9.BG.40Vyuntspakhkite-(Y)
    Y
     
    4
    		Al
     
    3
    		Si
     
    5
    		O
     
    18
    		(OH)
     
    5
    9.BG.45Dellaite
    Ca
     
    6
    		Si
     
    3
    		O
     
    11
    		(OH)
     
    2
    9.BG.50Gatelite-(Ce)
    CaCe
     
    3
    		Al
     
    2
    		(Al,Mg)(Mg,Fe
    2+
     
    		,Al)[(O,F)|(OH,O)
     
    2
    		|(SiO
     
    4
    		)
     
    3
    		|Si
     
    2
    		O
     
    7
    		]
    9.BG.55Västmanlandite-(Ce)
    Ca(Ce,La)
     
    3
    		Al
     
    2
    		Mg
     
    2
    		 [F|(OH)
     
    2
    		|(SiO
     
    4
    		)
     
    3
    		|Si
     
    2
    		O
     
    7
    		]
    Related Minerals - Hey's Index Grouping:
    16.21.1Esseneite
    CaFe
    3+
     
    		[AlSiO
     
    6
    		]
    16.21.3Ferrotschermakite
    ☐[Ca
     
    2
    		][Fe
    2+
    3
    		Fe
    3+
     
    		Al][(OH)
     
    2
    		|Al
     
    2
    		Si
     
    6
    		O
     
    22
    		]
    16.21.4Ferro-aluminotschermakite
    ☐[Ca
     
    2
    		][Fe
    2+
    3
    		Al
     
    2
    		][(OH)
     
    2
    		|Al
     
    2
    		Si
     
    6
    		O
     
    22
    		]
    16.21.5Ferritschermakite
    ☐[Ca
     
    2
    		][Mg
     
    3
    		Fe
    3+
    2
    		][(OH)
     
    2
    		|Al
     
    2
    		Si
     
    6
    		O
     
    22
    		]
    16.21.6Ferro-Ferritschermakite
    ☐[Ca
     
    2
    		][Fe
    2+
    3
    		Fe
    3+
    2
    		][(OH)
     
    2
    		|Al
     
    2
    		Si
     
    6
    		O
     
    22
    		]
    16.21.7Alumino-ferro-hornblende
    Ca
     
    2
    		Fe
     
    4
    		Al
     
    2
    		Si
     
    7
    		O
     
    22
    		(OH)
     
    2
    16.21.8Pumpellyite-(Fe2+)
    Ca
     
    2
    		Fe
    2+
     
    		Al
     
    2
    		[(OH)
     
    2
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		] · H
     
    2
    		O
    16.21.8Pumpellyite-(Fe3+)
    Ca
     
    2
    		(Fe
    3+
     
    		,Mg,Fe
    2+
     
    		)(Al,Fe
    3+
     
    		)
     
    2
    		[(OH,O)
     
    2
    		|SiO
     
    4
    		|Si
     
    2
    		O
     
    7
    		] · H
     
    2
    		O

    Other Names for Epidote

    Synonyms:
    AcanthiconeAcanticoneAcanticoniteAchmatiteAescherite
    AkanthiconeAllochiteArendaliteArenditeBucklandite (of Hermann)
    DelphiniteEpidosyteEpidotiteEscheriteFerriepidote
    FerriepidotoIron EpidoteOisanite (of de Saussure)PistacitePistazite
    PosstrevoritePuschkinitePushkiniteScorzaSelphinite
    Strahslstein (of Werner)Thallite
    German names:
    AcanthikonAcanticonitAcantikonitAchmatitAescherit
    AllochitArendalitArenditEisenepidotEpidot
    EpidotitEscheritPistacitPosstrevoritPuschkinit
    PushkinitSelphinitThallit
    Italian names:
    Epidoto
    Russian names:
    Эпидот
    Spanish names:
    AcanticonitaAchmatitaAescheritaAllochitaArendalita
    ArenditaEpidotitaEscheritaPistacitaPosstrevorita
    PuschkinitaPushkinitaSelphinitaThallita
    Traditional Chinese names:
    綠簾石
    Varieties:
    Allanite-EpidoteBeryllian EpidoteChrome-PistaziteTawmawiteWithamite

    Other Information

    Health Warning:No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

    References for Epidote

    Reference List:Dana, E.S. (1892) Dana's system of mineralogy, 6th. edition. New York: 516-521.

    Gottardi G. (1954)- Dati ed osservazioni sulla struttura dell'epidoto. Periodico di Mineralogia – Roma pp. 245-250.

    Seki, Y. (1959) Relation between chemical composition and lattice constants of epidote. American Mineralogist: 44: 720-730.

    Chatterjee, N.D. (1962) Vesuvianite-epidote paragenesis as a product of greenschist facies of regional metamorphism in the Western Alps. Beiträge zur Mineralogie und Petrographie: 8: 432-439.

    Keith, T.E.C., L.J.P. Muffler & M. Cremer (1968), Hydrothermal epidote formed in the Salton Sea geothermal system, California: American Mineralogist: 53: 1635-1644.

    Dollase, W.A. (1971), Refinement of the crystal structures of epidote, allanite and hancockite: American Mineralogist: 56: 447-464.

    Gabe, E.J., J.C. Portheine, and
    S.H. Whitlow (1973) A reinvestigation of the epidote structure: confirmation of the iron location. American Mineralogist: 58: 218-223.

    Sakai, C., Higashino, T., and Enami, M. (1984) REE-bearing epidote from Sanbagawa pelitic schists, central Shikoku, Japan. Geochem. Journal: 18: 45-53.

    Deer, W.A., R.A. Howie, and J. Zussman (1986) Rock-forming minerals, (2nd edition), v. 1B, disilicates and ring silicates: 44: 134.

    Kvick, Å, J.J. Pluth, J.W. Richardson, Jr., and J.V. Smith (1988) The ferric iron distribution and hydrogen bonding in epidote: a neutron diffraction study
    at 15 K. Acta Cryst.: 44: 351-355.

    Holland, T.J.B., Redfern, S.A.T., and Pawley, A.R. (1996), Volume behavior of hydrous minerals at high pressure and temperature: II. Compressibilities of lawsonite, zoisite, clinozoisite and epidote. American Mineralogist: 81: 341-348.

    Gieré, R. and Sorensen, S.S. (2004) Allanite and other REE-rich epidote-group minerals. In: Epidotes (A. Liebscher & G. Franz, editors). Rev. Mineral. Geochem.: 56: 431-493.

    Internet Links for Epidote

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    Localities for Epidote

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