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Pentagonite

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Big Photo

Wagholi Quarry, Wagholi, Pune District (Poonah District), Maharashtra, India
© Elmar Lackner 2009

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Formula:
Ca(VO)Si
 
4
O
 
10
 · 4H
 
2
O
System:OrthorhombicColour:Greenish blue
Hardness:3 - 4
Name:For the pseudosymmetrical five-fold habit of the typical pentagonite twins.
Dimorph of:Cavansite


Structurally related to plumbophyllite.

Ishida et al. (2009) suggest that cavansite is a low-temperature form and pentagonite a high-temperature form.

Classification of Pentagonite

IMA status:Approved
Strunz 8th edition ID:8/H.36-20
Nickel-Strunz 10th (pending) edition ID:9.EA.55

9 : SILICATES (Germanates)
E : Phyllosilicates
A : Single nets of tetrahedra with 4-, 5-, (6-), and 8-membered rings
Dana 8th edition ID:74.3.7.2

74 : PHYLLOSILICATES Modulated Layers
3 : Modulated Layers with joined strips
Hey's CIM Ref.:14.14.2

14 : Silicates not Containing Aluminum
14 : Silicates of V and Bi
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Type Occurrence of Pentagonite

Type Locality:Owyhee Dam, Lake Owyhee State Park, Malheur Co., Oregon, USA
Year of Discovery:1973

Occurrences of Pentagonite

Geological Setting:Fracture filling in tuffs and basalts.

Physical Properties of Pentagonite

Lustre:Vitreous
Diaphaneity (Transparency):Transparent
Colour:Greenish blue
Streak:Light blue
Hardness (Mohs):3 - 4
Tenacity:Brittle
Cleavage:Distinct/Good
Good on {010}
Density (calculated):2.33 g/cm3

Crystallography of Pentagonite

Crystal System:Orthorhombic
Class (H-M):mm2 - Pyramidal
Cell Parameters:a = 10.386(4) Å, b = 14.046(7) Å, c = 8.975(2) Å
Ratio:a:b:c = 0.739 : 1 : 0.639
Unit Cell Volume:V 1,309.29 ų (Calculated from Unit Cell)
Z:4
Morphology:Prismatic, bladed.
Twinning:Cyclical by reflection across {110}.
Comment:Space group Ccm21.

Optical Data of Pentagonite

Type:Biaxial (-)
RI values: nα = 1.533 nβ = 1.544 nγ = 1.547
2V:Measured: 50° , Calculated: 54°
Maximum Birefringence:δ = 0.014

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:Low
Dispersion:r > v strong
Pleochroism:Visible
Comments:X=Z= colourless
Y= blue

Chemical Properties of Pentagonite

Formula:
Ca(VO)Si
 
4
O
 
10
 · 4H
 
2
O
Essential elements:Ca, H, O, Si, V
All elements listed in formula:Ca, H, O, Si, V

Relationship of Pentagonite to other Species

Related Minerals - Nickel-Strunz Grouping):

- +
9.EA.05Cuprorivaite
CaCu[Si
 
4
O
 
10
]
9.EA.05Gillespite
BaFe
2+
 
[Si
 
4
O
 
10
]
9.EA.05Effenbergerite
BaCu[Si
 
4
O
 
10
]
9.EA.05Wesselsite
SrCu[Si
 
4
O
 
10
]
9.EA.10Ekanite
(Ca,Fe
2+
 
,Pb)
 
2
(Th,U)[Si
 
8
O
 
20
]
9.EA.15Apophyllite-(KF)
KCa
 
4
(Si
 
8
O
 
20
)(F,OH) · 8H
 
2
O
9.EA.15Apophyllite-(KOH)
KCa
 
4
(Si
 
8
O
 
20
)(OH,F) · 8H
 
2
O
9.EA.15Apophyllite-(NaF)
NaCa
 
4
(Si
 
8
O
 
20
)F · 8H
 
2
O
9.EA.20Magadiite
NaSi
 
7
O
 
13
(OH)
 
3
 · 3H
 
2
O
9.EA.25Dalyite
K
 
2
ZrSi
 
6
O
 
15
9.EA.25Davanite
K
 
2
TiSi
 
6
O
 
15
9.EA.30Sazhinite-(Ce)
Na
 
3
Ce[Si
 
6
O
 
15
] · 6H
 
2
O
9.EA.30Sazhinite-(La)
Na
 
3
La[Si
 
6
O
 
15
] · 2H
 
2
O
9.EA.35Armstrongite
CaZr[Si
 
6
O
 
15
] · 3H
 
2
O
9.EA.40Okenite
CaSi
 
2
O
 
5
 · 2H
 
2
O
9.EA.45Nekoite
Ca
 
3
Si
 
6
O
 
15
·7H
 
2
O
9.EA.50Cavansite
Ca(VO)Si
 
4
O
 
10
 · 4H
 
2
O
9.EA.60Penkvilksite
Na
 
4
Ti
 
2
Si
 
8
O
 
22
 · 4H
 
2
O
9.EA.60Tumchaite
Na
 
2
Zr(Si
 
4
O
 
11
) · 2H
 
2
O
9.EA.65Nabesite
Na
 
2
BeSi
 
4
O
 
10
 · 4H
 
2
O
9.EA.70Ajoite
(K,Na)Cu
 
7
AlSi
 
9
O
 
24
(OH)
 
6
 · 3H
 
2
O
9.EA.75Zeravshanite
Na
 
2
Cs
 
4
Zr
 
3
[Si
 
18
O
 
45
]*2H
 
2
O
9.EA.80Bussyite-(Ce)
(Ce,REE)
 
3
(Na,H
 
2
O)
 
6
MnSi
 
9
Be
 
5
(O,OH)
 
30
F
 
4
9.EA.85Plumbophyllite
Pb
 
2
Si
 
4
O
 
10
 · H
 
2
O
Related Minerals - Hey's Index Grouping:

- +
14.14.1Cavansite
Ca(VO)Si
 
4
O
 
10
 · 4H
 
2
O
14.14.3Goldmanite
Ca
 
3
V
3+
2
(SiO
 
4
)
 
3
14.14.4Haradaite
SrVSi
 
2
O
 
7
14.14.5Saneroite
Na
 
2
(Mn,Mn)
 
10
Si
 
11
VO
 
34
(OH)
 
4
14.14.6Erlianite
(Fe,Mg)
 
4
(Fe,V)
 
2
Si
 
6
O
 
15
(OH,O)
 
8
14.14.7Eulytine
Bi
 
4
(SiO
 
4
)
 
3
14.14.8Bismutoferrite
Fe
3+
2
Bi(SiO
 
4
)
 
2
(OH)

Other Names for Pentagonite

Synonyms:
IMA1971-039
Other Languages:
German:Pentagonit
Russian:Пентагонит
Spanish:Pentagonita

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 Pentagonite

Reference List:

- +
Staples, L.W., H.T. Evans, Jr., and J.R. Lindsay (1973): Cavansite and pentagonite, new dimorphous calcium vanadium silicate minerals from Oregon. Amer. Mineral., 58, 405-411.

Evans, H.T., Jr. (1973): The crystal structures of cavansite and pentagonite. Amer. Mineral., 58, 412-424.

Mineralogical Record (2003): 34: 40-43.

Ishida, N., Kimata, M., Nishida, N., Hatta, T., Shimizu, M., Akasaka, T. (2009): Polymorphic relation between cavansite and pentagonite: Genetic implications of oxonium ion in cavansite. Journal of Mineralogical and Petrological Sciences, 104, 241-252.

Danisi, R. M. , Armbruster, T., and Lazic B. (2012): In situ dehydration behavior of zeolite-like pentagonite: A single-crystal X-ray study. Journal of Solid State Chemistry 197,508-516.

Internet Links for Pentagonite

Search Engines:
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    • External Links:
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  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Pentagonite details from Handbook of Mineralogy (PDF)
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    • Localities for Pentagonite

    The 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.
    Hide Locality List
    (TL) indicates type locality. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.
    India
     
    • Maharashtra
      • Pune District (Poonah District)
        • Lonavale (Lonavala)
    		Praszkier, T. & Siuda, R. (2007): The Lonavala Quarry, Pune District, Maharashtra, India. Mineralogical Record 38: 185-189
        • Talegaon
    		Praszkier, T. (2009): Cavansit und Pentagonit aus Indien. Mineralien-Welt 20 (6), 16-25.
    Praszkier, T. (2009): Cavansit und Pentagonit aus Indien. Mineralien-Welt 20 (6), 16-25.
    http://www.irocks.com/pentag.htm
    USA
     
    • Oregon
      • Malheur Co.
        • Lake Owyhee State Park
    		Amer.Min.(1973) 58, 405-411 and 412-424
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