Pentagonite
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Formula:
CaV4+OSi4O10 · 4H2O
System:
Orthorhombic
Colour:
Greenish blue
Lustre:
Vitreous
Hardness:
3 - 4
Name:
For the pseudosymmetrical five-fold habit of the typical pentagonite twins.
Dimorph of:
Structurally related to plumbophyllite.
Ishida et al. (2009) suggest that cavansite is a low-temperature form and pentagonite a high-temperature form.
Ishida et al. (2009) suggest that cavansite is a low-temperature form and pentagonite a high-temperature form.
Classification of Pentagonite
Approved
8/H.36-20
9.EA.55
9 : SILICATES (Germanates)
E : Phyllosilicates
A : Single nets of tetrahedra with 4-, 5-, (6-), and 8-membered rings
9 : SILICATES (Germanates)
E : Phyllosilicates
A : Single nets of tetrahedra with 4-, 5-, (6-), and 8-membered rings
74.3.7.2
74 : PHYLLOSILICATES Modulated Layers
3 : Modulated Layers with joined strips
74 : PHYLLOSILICATES Modulated Layers
3 : Modulated Layers with joined strips
14.14.2
14 : Silicates not Containing Aluminum
14 : Silicates of V and Bi
14 : Silicates not Containing Aluminum
14 : Silicates of V and Bi
Physical Properties of Pentagonite
Vitreous
Diaphaneity (Transparency):
Transparent
Colour:
Greenish blue
Streak:
Light blue
Hardness (Mohs):
3 - 4
Tenacity:
Brittle
Cleavage:
Distinct/Good
Good on {010}
Good on {010}
Density:
2.33 g/cm3 (Calculated)
Optical Data of Pentagonite
Type:
Biaxial (-)
RI values:
nα = 1.533 nβ = 1.544 nγ = 1.547
2V:
Measured: 50° , Calculated: 54°
Max Birefringence:
δ = 0.014
Image 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
Y= blue
Chemical Properties of Pentagonite
IMA Formula:
CaV4+OSi4O10 · 4H2O
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.
Occurrences of Pentagonite
Type Occurrence of Pentagonite
Relationship of Pentagonite to other Species
| 9.EA.05 | Cuprorivaite | CaCuSi4O10 |
| 9.EA.05 | Gillespite | BaFe2+Si4O10 |
| 9.EA.05 | Effenbergerite | BaCuSi4O10 |
| 9.EA.05 | Wesselsite | SrCuSi4O10 |
| 9.EA.10 | Ekanite | Ca2ThSi8O20 |
| 9.EA.15 | Fluorapophyllite-(K) | KCa4Si8O20F · 8H2O |
| 9.EA.15 | Hydroxyapophyllite-(K) | KCa4Si8O20(OH,F) · 8H2O |
| 9.EA.15 | Fluorapophyllite-(Na) | NaCa4Si8O20F · 8H2O |
| 9.EA.20 | Magadiite | Na2Si14O29 · 11H2O |
| 9.EA.25 | Dalyite | K2ZrSi6O15 |
| 9.EA.25 | Davanite | K2TiSi6O15 |
| 9.EA.30 | Sazhinite-(Ce) | Na3CeSi6O15 · 2H2O |
| 9.EA.30 | Sazhinite-(La) | Na3LaSi6O15 · 2H2O |
| 9.EA.35 | Armstrongite | CaZrSi6O15 · 2H2O |
| 9.EA.40 | Okenite | Ca10Si18O46 · 18H2O |
| 9.EA.45 | Nekoite | Ca3Si6O15 · 7H2O |
| 9.EA.50 | Cavansite | CaV4+OSi4O10 · 4H2O |
| 9.EA.60 | Penkvilksite | Na4Ti2Si8O22 · 4H2O |
| 9.EA.60 | Tumchaite | Na2ZrSi4O11 · 2H2O |
| 9.EA.65 | Nabesite | Na2BeSi4O10 · 4H2O |
| 9.EA.70 | Ajoite | K3Cu202+Al3Si29O76(OH)16 · 8H2O |
| 9.EA.75 | Zeravshanite | Na2Cs4Zr3Si18O45 · 2H2O |
| 9.EA.80 | Bussyite-(Ce) | (Na,H2O)6(Ce,REE)3Be5MnSi9(O,OH)30F4 |
| 9.EA.85 | Plumbophyllite | Pb2Si4O10 · H2O |
| 14.14.1 | Cavansite | CaV4+OSi4O10 · 4H2O |
| 14.14.3 | Goldmanite | Ca3V23+(SiO4)3 |
| 14.14.4 | Haradaite | SrV4+Si2O7 |
| 14.14.5 | Saneroite | Na2(Mn2+,Mn3+)10V5+Si11O34(OH)4 |
| 14.14.6 | Erlianite | Fe42+Fe23+Si6O15(OH)8 |
| 14.14.7 | Eulytine | Bi4(SiO4)3 |
| 14.14.8 | Bismutoferrite | Fe23+Bi(SiO4)2(OH) |
Other Names for Pentagonite
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 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.
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
mindat.org URL:
https://www.mindat.org/min-3152.html
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Specimens:
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Localities for Pentagonite
This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the 
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(TL) indicates type locality for a valid mineral species. (FRL) indicates first recorded locality for everything else. ? 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 | |
| Praszkier, T. & Siuda, R. (2007): The Lonavala Quarry, Pune District, Maharashtra, India. Mineralogical Record 38: 185-189 |
| 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 (TL) | |
| Amer.Min.(1973) 58, 405-411 and 412-424 |
Wagholi Quarries, Wagholi, Pune District, Maharashtra, India