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Piemontite

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Formula:
{Ca2}{Al2Mn3+}(Si2O7)(SiO4)O(OH)
System:
Monoclinic
Colour:
Red, red-violet, ...
Hardness:
6 - 6½
Name:
Named in 1853 by Gustav Adolph Kenngott for the type locality, the Piemonte region of Italy.
Clinozoisite Subgroup of the Epidote Group.

"Piemontite" has two different uses: Piemontite (sensu stricto) is the mineral species described here, but more commonly "piemontite" refers incorrectly to deep red colored, Mn3+-bearing epidotes that are really varieties of the species epidote, and not strictly speaking the *species* piemontite. "Piemontites" rarely contain more than 40% of the piemontite molecule, so many "piemontites" in collections (and pictured here in Mindat) are really Mn-rich red varieties of epidote. (See for example: Ashley (1984), Kawachi et al. (1983), and Martin & Lombardo (1995).)

Classification of Piemontite

Approved
9.BG.05

9 : SILICATES (Germanates)
B : Sorosilicates
G : Sorosilicates with mixed SiO4 and Si2O7 groups; cations in octahedral [6] and greater coordination
58.2.1a.11

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)
16.16.22

16 : Silicates Containing Aluminum and other Metals
16 : Aluminosilicates of Mn
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First Recorded Occurrence of Piemontite

Year of Discovery:
1853

Occurrences of Piemontite

Geological Setting:
Greenschist to amphibolite grade regional metamorphism, metasomatised manganese deposits, low temperature hydrothermal veins.

Physical Properties of Piemontite

Vitreous
Diaphaneity (Transparency):
Translucent, Opaque
Colour:
Red, red-violet, red-brown to reddish black
Streak:
Reddish
Hardness (Mohs):
6 - 6½
Tenacity:
Brittle
Cleavage:
Perfect
Perfect on {001}
Poor on {100}
Fracture:
Irregular/Uneven
Density:
3.46 - 3.54 g/cm3 (Measured)    3.45 g/cm3 (Calculated)

Crystallography of Piemontite

Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/m
Cell Parameters:
a = 8.878(10) Å, b = 5.692(5) Å, c = 10.201(10) Å
β = 115.25°
Ratio:
a:b:c = 1.56 : 1 : 1.792
Unit Cell Volume:
V 466.24 ų (Calculated from Unit Cell)
Z:
2
Morphology:
Prismatic, bladed or acicular crystals.
Twinning:
{100} uncommon, lamellar

Optical Data of Piemontite

Type:
Biaxial (+)
RI values:
nα = 1.725 - 1.756 nβ = 1.730 - 1.789 nγ = 1.750 - 1.832
2V:
Measured: 50° to 86°, Calculated: 54° to 86°
Max Birefringence:
δ = 0.025 - 0.076
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:
High
Dispersion:
r > v strong
Pleochroism:
Visible
Comments:
X= light yellow, orange to pink
Y= pale violet to deep lavender
Z= pink to deep red

Chemical Properties of Piemontite

Formula:
{Ca2}{Al2Mn3+}(Si2O7)(SiO4)O(OH)
Essential elements:
All elements listed in formula:
Common Impurities:
Fe,Ti,Na,K,H2O

Relationship of Piemontite to other Species

Other Members of Group:
Clinozoisite{Ca2}{Al3}(Si2O7)(SiO4)O(OH)
Clinozoisite-(Sr){CaSr}{Al3}(Si2O7)(SiO4)O(OH)
Epidote{Ca2}{Al2Fe3+}(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-(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.05aEpidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
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-(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
16.16.1KanonaiteMn3+Al(SiO4)O
16.16.2SpessartineMn32+Al2(SiO4)3
16.16.3DavreuxiteMnAl6Si4O17(OH)2
16.16.4SursassiteMn22+Al3(Si2O7)(SiO4)(OH)3
16.16.5CarpholiteMn2+Al2(Si2O6)(OH)4
16.16.6KellyiteMn22+Al(AlSiO5)(OH)4
16.16.7PennantiteMn52+Al(AlSi3O10)(OH)8
16.16.8Akatoreite(Mn2+,Fe2+)9Al2(HSi4O13)2(OH)6
16.16.9Ganophyllite(K,Na,Ca)2Mn8(Si,Al)12(O,OH)32 · 8H2O
16.16.10Mangano-ferri-eckermannite[Na][Na2][Mn42+(Fe3+)]Si8O22(OH)2
16.16.11Masutomilite(K,Rb)(Li,Mn3+,Al)3(AlSi3O10)(F,OH)2
16.16.13HowieiteNa(Fe,Mn)10(Fe,Al)2Si12O31(OH)13
16.16.14Eggletonite(Na,K,Ca)2(Mn,Fe)8(Si,Al)12O29(OH)7 · 11H2O
16.16.15BannisteriteCa0.5(K,Na)0.5(Mn,Fe,Zn)10(Si,Al)16O38(OH)8 · 5.5H2O
16.16.16Taneyamalite(Na,Ca)(Mn,Mg,Fe)12Si12(O,OH)44
16.16.17ZussmaniteK(Fe,Mg,Mn)13(Si,Al)18O42(OH)14
16.16.18CoombsiteK(Mn,Fe,Mg)13(Si,Al)18O42(OH)14
16.16.19HenritermieriteCa3(Mn3+,Al)2(SiO4)2(OH)4
16.16.20MacfalliteCa2(Mn3+,Al)3(Si2O7)(SiO4)(OH)3
16.16.21Ottrélite(Mn2+,Fe2+,Mg)Al2(SiO4)O(OH)2
16.16.23OkhotskiteCa2(Mn2+,Mg)(Mn3+,Al,Fe3+)2(Si2O7)(SiO4)(OH)2 · H2O
16.16.24Pumpellyite-(Mn2+)Ca2(Mn2+,Mg)(Al,Mn3+,Fe3+)2(Si2O7)(SiO4)(OH)2 · H2O
16.16.25Piemontite-(Sr){CaSr}{Al2Mn3+}(Si2O7)(SiO4)O(OH)

Other Names for Piemontite

Name in Other Languages:

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 Piemontite

Reference List:
Short, Allan McIlroy (1933), A chemical and optical study of Piedmontite from Shadow Lake, Madera County, California: American Mineralogist: 18: 493-500.

American Mineralogist (1969): 54: 710-717.

Kawachi et al (1983) Journal of Metamorphic Geology, 1, 353-371.

Ashley, P.M. (1984) Australian Journal of Earth Sciences, 31, 203-216.

Bonazzi, P., Garbarino, C., and Menchetti, S. (1992) Crystal chemistry of piemontites: REE-bearing piemontite from Monte Brugiana, Alpi Apuane, Italy. European Journal of Mineralogy: 4: 23.

Bermanec, V., Armbruster, T., Oberhänsli, R., and Zebec, V. (1994) Crystal chemistry of Pb- and REE-rich piemontite from Nezilovo, macedonia. Schweizerische mineralogische und petrographische Mitteilungen (1994): 74: 321-328.

Bonazzi, P. and Menchetti, S. (1994) Structural variations induced by heat treatment in allanite and REE-bearing piemontite. American Mineralogist: 79: 1176-1184.

Martin & Lombardo (1995) Museo Regionale Di Scienze Naturali, 13, 103-126.

Bonazzi, P., Menchetti, S., and Reinecke, T. (1996) Solid solution between piemontite and androsite-(La), a new mineral of the epidote group from Andros Island, Greece. American Mineralogist: 81: 735-742.

Langer, K., Tillmanns, E., Kersten, M., Almen, H., and Arni, R.K. (2002) The crystal chemistry of Mn3+ in the clino- and orthozoisite structure types, Ca2M3 3+[OH|O|SiO4|Si2O7]: A structural and spectroscopic study of some natural piemontites and "thulites" and their synthetic equivalents. Zeitschrift für Kristallographie: 217: 563-580.

Internet Links for Piemontite

Localities for Piemontite

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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