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Epidote

This page kindly sponsored by Gerhard Niklasch
Formula:
{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
System:
Monoclinic
Colour:
Yellowish-green, green, ...
Lustre:
Vitreous, Pearly
Hardness:
6
Name:
Named in 1801 by Rene Just Haüy from the Greek επιδοσιζ "Epidosis" = "increase" in allusion to the crystal characteristic of one longer side at the base of the prism.

Classification of Epidote

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
9.BG.05a

9 : SILICATES (Germanates)
B : Sorosilicates
G : Sorosilicates with mixed SiO4 and Si2O7 groups; cations in octahedral [6] and greater coordination
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)
16.21.2

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

Year of Discovery:
1801

Occurrences of Epidote

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

Physical Properties of Epidote

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:
3.38 - 3.49 g/cm3 (Measured)    3.43(3) g/cm3 (Calculated)

Crystallography of Epidote

Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/m
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 35 cm. Fibrous, coarse to fine granular, massive.
Twinning:
On {100}, contact, lamellar, common.

Crystallographic forms of Epidote

Crystal Atlas:
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Epidote no.9 - Goldschmidt (1913-1926)
Epidote no.94 - Goldschmidt (1913-1926)
3d models and HTML5 code kindly provided by www.smorf.nl.

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Crystal Structure

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:
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°
Max Birefringence:
δ = 0.019 - 0.046
Image 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:
{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Essential elements:
All elements listed in formula:
Common Impurities:
Al,Mg,Mn

Relationship of Epidote to other Species

Series:
Forms a series with Clinozoisite (see here)
Other Members of Group:
Clinozoisite{Ca2}{Al3}(Si2O7)(SiO4)O(OH)
Clinozoisite-(Sr){CaSr}{Al3}(Si2O7)(SiO4)O(OH)
Epidote-(Pb){CaPb}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Epidote-(Sr){CaSr}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Hancockite{CaPb}{Al2(Fe3+,Mn3+)}(Si2O7)(SiO4)O(OH)
Manganipiemontite-(Sr){CaSr}{Mn3+AlMn3+}(Si2O7)(SiO4)O(OH)
Mukhinite{Ca2}{Al2V3+}(Si2O7)(SiO4)O(OH)
Piemontite{Ca2}{Al2Mn3+}(Si2O7)(SiO4)O(OH)
Piemontite-(Pb)CaPbAl2Mn3+[Si2O7][SiO4]O(OH)
Piemontite-(Sr){CaSr}{Al2Mn3+}(Si2O7)(SiO4)O(OH)
9.BG.05bAllanite-(Ce){CaCe}{Al2Fe2+}(Si2O7)(SiO4)O(OH)
9.BG.05bAllanite-(La){CaLa}{Al2Fe2+}(Si2O7)(SiO4)O(OH)
9.BG.05bAllanite-(Y){CaY}{Al2Fe2+}(Si2O7)(SiO4)O(OH)
9.BG.05aClinozoisite{Ca2}{Al3}(Si2O7)(SiO4)O(OH)
9.BG.05bDissakisite-(Ce){CaCe}{Al2Mg}(Si2O7)(SiO4)O(OH)
9.BG.05Dollaseite-(Ce){CaCe}{MgAlMg}(Si2O7)(SiO4)(OH)F
9.BG.05Epidote-(Pb){CaPb}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
9.BG.05Khristovite-(Ce){CaCe}{MgAlMn2+}(Si2O7)(SiO4)(OH)F
9.BG.05Mukhinite{Ca2}{Al2V3+}(Si2O7)(SiO4)O(OH)
9.BG.05Piemontite{Ca2}{Al2Mn3+}(Si2O7)(SiO4)O(OH)
9.BG.05Piemontite-(Sr){CaSr}{Al2Mn3+}(Si2O7)(SiO4)O(OH)
9.BG.05bManganiandrosite-(La){Mn2+La}{Mn3+AlMn2+}(Si2O7)(SiO4)O(OH)
9.BG.05Tawmawite{Ca2}{(Al,Fe3+,Cr)3}(Si2O7)(SiO4)O(OH)
9.BG.05Manganipiemontite-(Sr){CaSr}{Mn3+AlMn3+}(Si2O7)(SiO4)O(OH)
9.BG.05bFerriallanite-(Ce){CaCe}{Fe3+AlFe2+}(Si2O7)(SiO4)O(OH)
9.BG.05Clinozoisite-(Sr){CaSr}{Al3}(Si2O7)(SiO4)O(OH)
9.BG.05Manganiandrosite-(Ce){(Mn2+,Ca)(Ce,REE)}{Mn3+AlMn2+}(Si2O7)(SiO4)O(OH)
9.BG.05Dissakisite-(La){CaLa}{Al2Mg}(Si2O7)(SiO4)O(OH)
9.BG.05Vanadoandrosite-(Ce){Mn2+Ce}{V3+AlMn2+}(Si2O7)(SiO4)O(OH)
9.BG.05Uedaite-(Ce){Mn2+Ce}{Al2Fe2+}(Si2O7)(SiO4)O(OH)
9.BG.05Epidote-(Sr){CaSr}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
9.BG.05bAllanite-(Nd){CaNd}{Al2Fe2+}(Si2O7)(SiO4)O(OH)
9.BG.05bFerriallanite-(La){CaLa}{Fe3+AlFe2+}(Si2O7)(SiO4)O(OH)
9.BG.05bÅskagenite-(Nd){Mn2+Nd}{Al2Fe3+}(Si2O7)(SiO4)O2
9.BG.10Zoisite{Ca2}{Al3}(Si2O7)(SiO4)O(OH)
9.BG.15MacfalliteCa2(Mn3+,Al)3(Si2O7)(SiO4)(OH)3
9.BG.15SursassiteMn22+Al3(Si2O7)(SiO4)(OH)3
9.BG.20Julgoldite-(Fe2+)Ca2(Fe2+,Mg)(Fe3+,Al)2(Si2O7)(SiO4)(OH)2 · H2O
9.BG.20OkhotskiteCa2(Mn2+,Mg)(Mn3+,Al,Fe3+)2(Si2O7)(SiO4)(OH)2 · H2O
9.BG.20Pumpellyite-(Fe2+)Ca2Fe2+Al2(Si2O7)(SiO4)(OH)2 · H2O
9.BG.20Pumpellyite-(Fe3+)Ca2(Fe3+,Mg,Fe2+)(Al,Fe3+)2(Si2O7)(SiO4)(OH,O)2 · H2O
9.BG.20Pumpellyite-(Mg)Ca2MgAl2(Si2O7)(SiO4)(OH)2 · H2O
9.BG.20Pumpellyite-(Mn2+)Ca2(Mn2+,Mg)(Al,Mn3+,Fe3+)2(Si2O7)(SiO4)(OH)2 · H2O
9.BG.20ShuiskiteCa2(Mg,Al)(Cr,Al)2(Si2O7)(SiO4)(OH)2 · 2H2O
9.BG.20Julgoldite-(Fe3+)Ca2(Fe3+,Mg)(Fe3+,Al)2(Si2O7)(SiO4)(OH,O)2 · H2O
9.BG.20Pumpellyite-(Al)Ca2(Al,Fe2+,Mg)Al2(Si2O7)(SiO4)(OH,O)2 · H2O
9.BG.20PoppiiteCa2(V3+,Fe3+,Mg)(V3+,Al)2(Si2O7)(SiO4)(OH,O)2 · H2O
9.BG.20Julgoldite-(Mg)Ca2(Mg,Fe2+)(Fe3+,Al)2(Si2O7)(SiO4)(OH)2 · H2O
9.BG.25GanomalitePb9Ca5Mn(Si2O7)4(SiO4)O
9.BG.30RustumiteCa10(Si2O7)2(SiO4)(OH)2Cl2
9.BG.35Vesuvianite(Ca,Na,☐)19(Al,Mg,Fe3+)13(☐,B,Al,Fe3+)5(Si2O7)4(SiO4)10(OH,F,O)10
9.BG.35WiluiteCa19(Al,Mg)13(B,☐,Al)5(Si2O7)4(SiO4)10(O,OH)10
9.BG.35ManganvesuvianiteCa19Mn3+(Al,Mn3+,Fe3+)10(Mg,Mn2+)2(Si2O7)4(SiO4)10O(OH)9
9.BG.35FluorvesuvianiteCa19(Al,Mg,Fe2+)13(Si2O7)4(SiO4)10O(F,OH)9
9.BG.40Vyuntspakhkite-(Y)(Y,Yb)4Al2.5-1.5(Si,Al)1.5-2.5(SiO4)4O(OH)7
9.BG.45DellaiteCa6(Si2O7)(SiO4)(OH)2
9.BG.50Gatelite-(Ce)CaCe3Al2(Al,Mg)(Mg,Fe2+,Al)(Si2O7)(SiO4)3(O,F)(OH,O)2
9.BG.55Västmanlandite-(Ce)Ca(Ce,La)3Al2Mg2(Si2O7)(SiO4)3(OH)2F
16.21.1EsseneiteCaFe3+[AlSiO6]
16.21.3Ferro-tschermakite☐{Ca2}{Fe32+Al2}(Al2Si6O22)(OH)2
16.21.4Ferro-aluminotschermakite☐{Ca2}{Fe32+Al2}(Al2Si6O22)(OH)2
16.21.5Ferri-tschermakite☐{Ca2}{Mg3Fe23+}(Al2Si6O22)(OH)2
16.21.6Ferro-Ferri-tschermakite☐{Ca2}{Fe32+Fe23+}(Al2Si6O22)(OH)2
16.21.7Alumino-ferro-hornblende☐{Ca2}{Fe42+Al}(AlSi7O22)(OH)2
16.21.8Pumpellyite-(Fe2+)Ca2Fe2+Al2(Si2O7)(SiO4)(OH)2 · H2O
16.21.8Pumpellyite-(Fe3+)Ca2(Fe3+,Mg,Fe2+)(Al,Fe3+)2(Si2O7)(SiO4)(OH,O)2 · H2O

Other Names for Epidote

Other Information

Health Risks:
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.

Armbruster, T., Bonazzi, P., Akasaka, M., Bermanec, V., Chopin, C., Gieré R., Heuss-Assbichler, S., Liebscher, A., Menchetti, S., Pan, Y., Pasero, M. (2006): Recommended nomenclature of epidote-group minerals. European Journal of Mineralogy, 18, 551-567.

Internet Links for Epidote

Specimens:
The following Epidote specimens are currently listed for sale on minfind.com.

Localities for Epidote

map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
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