Pentagonite
A valid IMA mineral species
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About Pentagonite
Formula:
Ca(VO)Si4O10 · 4H2O
Colour:
Greenish blue
Lustre:
Vitreous
Hardness:
3 - 4
Specific Gravity:
2.33 (Calculated)
Crystal System:
Orthorhombic
Name:
For the pseudosymmetrical five-fold habit of the typical pentagonite twins. Note that "characteristic pentagonite fivelings are not formed from five, but from six individuals." (Ottens et al., 2025).
Dimorph of:
Structurally related to plumbophyllite.
Ishida et al. (2009) suggest that cavansite is a low-temperature form and pentagonite a high-temperature form. Conditions of formation of both dimorphs are discussed in Ottens et al. (2025).
To distinguish pentagonite and cavansite one can compare the two under light with a strong blue component, like halogen or sunlight. The pentagonite is a very pure blue and the cavansite is green in comparison. The teal colour of cavansite may not show up in photos but it is real. Please see: https://www.mindat.org/mesg-609416.html#609580
Ishida et al. (2009) suggest that cavansite is a low-temperature form and pentagonite a high-temperature form. Conditions of formation of both dimorphs are discussed in Ottens et al. (2025).
To distinguish pentagonite and cavansite one can compare the two under light with a strong blue component, like halogen or sunlight. The pentagonite is a very pure blue and the cavansite is green in comparison. The teal colour of cavansite may not show up in photos but it is real. Please see: https://www.mindat.org/mesg-609416.html#609580
Unique Identifiers
Mindat ID:
3152
Long-form identifier:
mindat:1:1:3152:9
IMA Classification of Pentagonite
Approved
IMA Formula:
CaV4+OSi4O10 · 4H2O
First published:
1973
Classification of Pentagonite
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
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
| Symbol | Source | Reference |
|---|---|---|
| Ptg | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Physical Properties of Pentagonite
Vitreous
Transparency:
Transparent
Colour:
Greenish blue
Streak:
Light blue
Hardness:
3 - 4 on Mohs scale
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
Based on recorded range of RI values above.
Based on recorded range of RI values above.
Interference Colours:
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars.
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars.
Surface Relief:
Moderate
Dispersion:
r > v strong. Dispersion opposite to that of cavansite.
Optical Extinction:
X = b; Y = a; Z = c.
Pleochroism:
Visible
Comments:
X=Z= colourless
Y= blue
Y= blue
Chemistry of Pentagonite
Mindat Formula:
Ca(VO)Si4O10 · 4H2O
Element Weights:
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 V:
1,309.29 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Prismatic, bladed.
Twinning:
Cyclical by reflection across {110}, producing twinning at an angle near 72.7° ((110) ∧ (110)), and sometimes giving rise to fivelings. Note that "characteristic pentagonite fivelings are not formed from five, but from six individuals." (Ottens et al., 2025).
Comment:
Space group Ccm21.
Crystal Structure
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Data courtesy of the American Mineralogist Crystal Structure Database. Click on an AMCSD ID to view structure
| ID | Species | Reference | Link | Year | Locality | Pressure (GPa) | Temp (K) |
|---|---|---|---|---|---|---|---|
| 0000317 | Pentagonite | Evans H T (1973) The crystal structures of cavansite and pentagonite American Mineralogist 58 412-424 |  | 1973 | 0 | 293 | |
| 0019265 | Pentagonite | Ishida N, Kimata M, Nishida N, Hatta T, Shimizu M, Akasaka T (2009) Polymorphic relation between cavanite and pentagonite: genetic implications of oxonium ion in cavansite Journal of Mineralogical and Petrological Sciences 104 241-252 | 2009 | Deccan basalts, Wagholi, India | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 6.071 Å | (100) |
| 3.920 Å | (100) |
| 3.755 Å | (100) |
| 8.298 Å | (70) |
| 3.500 Å | (36) |
| 2.569 Å | (36) |
| 4.446 Å | (25) |
Comments:
Owyhee Dam, Oregon, USA. Data from the type description.
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 3b: Earth’s earliest hydrosphere | >4.45 |
| 16 : Low-? aqueous alteration of Hadean subaerial lithologies (see also #23) |
Geological Setting:
Fracture filling in tuffs and basalts.
Type Occurrence of Pentagonite
General Appearance of Type Material:
Radiating greenish-blue prismatic crystals.
Place of Conservation of Type Material:
National Museum of Natural History, Washington, D.C., USA, 120584, 122769.
Geological Setting of Type Material:
Cavities and veinlets in basalt and vugs in tuff.
Associated Minerals at Type Locality:
Synonyms of Pentagonite
Other Language Names for Pentagonite
Common Associates
Associated Minerals Based on Photo Data:
| 84 photos of Pentagonite associated with Heulandite Subgroup | (Na/Ca/K)5-6[Al8-9 Si27-28 O72] · nH2O |
| 75 photos of Pentagonite associated with Stilbite-Ca | NaCa4(Si27Al9)O72 · 28H2O |
| 74 photos of Pentagonite associated with Calcite | CaCO3 |
| 68 photos of Pentagonite associated with Mordenite | (Na2,Ca,K2)4(Al8Si40)O96 · 28H2O |
| 63 photos of Pentagonite associated with Stilbite Subgroup | M6-7[Al8-9Si27-28O72] · nH2O |
| 20 photos of Pentagonite associated with Cavansite | Ca(VO)Si4O10 · 4H2O |
| 9 photos of Pentagonite associated with Quartz | SiO2 |
| 8 photos of Pentagonite associated with Heulandite-Ca | (Ca,Na)5(Si27Al9)O72 · 26H2O |
| 7 photos of Pentagonite associated with Apophyllite Group | AB4[Si8O22]X · 8H2O |
| 5 photos of Pentagonite associated with Gyrolite | NaCa16Si23AlO60(OH)8 · 14H2O |
Related Minerals - Strunz-mindat Grouping
| 9.EA. | Hydroxymcglassonite-(K) | KSr4Si8O20(OH) · 8H2O |
| 9.EA. | Miyawakiite-(Y) | ◻Y4Fe2(Si8O20)(CO3)4(H2O)3 |
| 9.EA. | Bussyite-(Y) | (Y,REE,Ca)3(Na,Ca)6MnSi9Be5(O,OH,F)34 |
| 9.EA. | Fluorapophyllite-(NH4) | NH4Ca4(Si8O20)F · 8H2O |
| 9.EA.05 | Gillespite | BaFe2+Si4O10 |
| 9.EA.05 | Cuprorivaite | CaCuSi4O10 |
| 9.EA.05 | Wesselsite | SrCuSi4O10 |
| 9.EA.05 | Effenbergerite | BaCuSi4O10 |
| 9.EA.07 | Fluorapophyllite-(Cs) | CsCa4(Si8O20)F · 8H2O |
| 9.EA.10 | Ekanite | Ca2ThSi8O20 |
| 9.EA.15 | Fluorapophyllite-(Na) | NaCa4(Si8O20)F · 8H2O |
| 9.EA.15 | Fluorapophyllite-(K) | KCa4(Si8O20)(F,OH) · 8H2O |
| 9.EA.15 | Hydroxyapophyllite-(K) | KCa4(Si8O20)(OH,F) · 8H2O |
| 9.EA.20 | Magadiite | Na2Si14O29 · 11H2O |
| 9.EA.25 | Dalyite | K2ZrSi6O15 |
| 9.EA.25 | Davanite | K2TiSi6O15 |
| 9.EA.30 | Sazhinite-(La) | Na3La[Si6O15] · 2H2O |
| 9.EA.30 | Sazhinite-(Ce) | Na3CeSi6O15 · 2H2O |
| 9.EA.35 | Armstrongite | CaZr[Si6O15] · 3H2O |
| 9.EA.40 | Okenite | Ca10Si18O46 · 18H2O |
| 9.EA.45 | Perettiite-(Y) | Y2Mn4FeSi2B8O24 |
| 9.EA.45 | Nekoite | Ca3Si6O15 · 7H2O |
| 9.EA.45 | Badakhshanite-(Y) | Y2Mn4Al(Si2B7BeO24) |
| 9.EA.47 | Shlykovite | KCa[Si4O9(OH)] · 3H2O |
| 9.EA.50 | Diegogattaite | Na2CaCu2Si8O20 · H2O |
| 9.EA.50 | Cavansite | Ca(VO)Si4O10 · 4H2O |
| 9.EA.52 | Yangite | PbMnSi3O8 · H2O |
| 9.EA.60 | Penkvilksite | Na4Ti2Si8O22 · 4H2O |
| 9.EA.60 | Tumchaite | Na2Zr(Si4O11) · 2H2O |
| 9.EA.65 | Nabesite | Na2BeSi4O10 · 4H2O |
| 9.EA.70 | Ajoite | (K,Na)Cu7AlSi9O24(OH)6 · 3H2O |
| 9.EA.75 | Zeravshanite | Na2Cs4Zr3[Si18O45]*2H2O |
| 9.EA.80 | Bussyite-(Ce) | (Ce,REE)3(Na,H2O)6MnSi9Be5(O,OH)30F4 |
| 9.EA.85 | Plumbophyllite | Pb2Si4O10 · H2O |
Other Information
Notes:
Soluble in acids with difficulty. In HNO3, the blue color bleaches out and turns olive brown. A fine white crystalline precipitate is slowly formed on a microscope slide when the minerals are heated in dilute H2SO4.
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.
Internet Links for Pentagonite
mindat.org URL:
https://www.mindat.org/min-3152.html
Please feel free to link to this page.
Please feel free to link to this page.
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References for Pentagonite
Reference List:
Staples, Lloyd W., Evans, Howard T., Lindsay, and James R. (1973) Cavansite and pentagonite, new dimorphous calcium vanadium silicate minerals from Oregon. American Mineralogist, 58 (5-6) 405-411
Evans, Howard T., Jr. (1973) The crystal structures of cavansite and pentagonite. American Mineralogist, 58 (5-6) 412-424
White, John (2002) Let's Get It Right: Cavansite or Pentagonite? Rocks & Minerals, 77 (4). 274-275 doi:10.1080/00357529.2002.9925646
Ishida, Naoya, Kimata, Mitsuyoshi, Nishida, Norimasa, Hatta, Tamao, Shimizu, Masahiro, Akasaka, Takeshi (2009) Polymorphic relation between cavansite and pentagonite: Genetic implications of oxonium ion in cavansite. Journal of Mineralogical and Petrological Sciences, 104 (4) 241-252 doi:10.2465/jmps.070724b
Frost, Ray L., Xi, Yunfei (2012) Vibrational spectroscopic study of the minerals cavansite and pentagonite Ca(V4+O)Si4O10·4H2O. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 95. 263-269 doi:10.1016/j.saa.2012.04.021
Localities for Pentagonite
symbol to view information about a locality.
The Locality List
- This locality has map coordinates listed.
- This locality has estimated coordinates.
ⓘ - Click for references and further information on this occurrence.
? - Indicates mineral may be doubtful at this locality.
- Good crystals or important locality for species.
- World class for species or very significant.
(TL) - Type Locality for a valid mineral species.
(FRL) - First Recorded Locality for everything else (eg varieties).
All localities listed without proper references should be considered as questionable.
India | |
| Praszkier et al. (2007) +1 other reference |
| Praszkier (2009) |
| Praszkier (2009) | |
| www.irocks.com (2002) +1 other reference | |
New Zealand | |
| Collection of RJ Martin |
USA (TL) | |
| Staples et al. (1973) +1 other reference |
Quick NavTopAbout PentagoniteUnique IdentifiersIMA Classification Classification Mineral SymbolsPhysical Properties Optical Data Chemistry Crystallography Crystal StructureX-Ray Powder DiffractionGeological EnvironmentType Occurrence SynonymsOther LanguagesCommon AssociatesStrunz-MindatOther InformationInternet Links References Localities Locality List
Wagholi Quarries, Wagholi, Pune District, Pune Division, Maharashtra, India