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(H2O)3·H2O
Approval year:
1971
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 for Standard |
|---|---|---|
| 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. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
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. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
Surface Relief:
None to Very Low
Relative to Canada balsam mounting medium (n ≈ 1.537).
Relative to Canada balsam mounting medium (n ≈ 1.537).
This shows the grain boundary and Becke line effect under plane-polarised
light, based on the contrast between this mineral's average refractive
index and the mounting medium. It does not take into account mineral
colouration.
In focus
Interference Figure:
This shows the idealized biaxial acute bisectrix (Bxa) interference figure
- the conoscopic view for a grain cut perpendicular to the acute bisectrix, using
this mineral's 2V. The two small white dots mark the melatopes - the points
where the two optic axes emerge - and are shown only when they fall within the
field of view. The coloured bands are isochromatics, and the dark bands are
isogyres.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
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
Load
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Show
Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
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Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
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View
CIF File Best | x | y | z | a | b | c
CIF File Best | x | y | z | a | b | c
Rotation
Stop | Start
Stop | Start
Labels
Console Off | On | Grey | Yellow
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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) |
|---|---|---|---|---|---|---|---|
| 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 | |
| 0000317 | Pentagonite | Evans H T (1973) The crystal structures of cavansite and pentagonite American Mineralogist 58 412-424 |  | 1973 | 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
Associations Based on Photo Data:
| 86 photos of Pentagonite associated with Heulandite Subgroup | (Na/Ca/K)5-6[Al8-9 Si27-28 O72] · nH2O |
| 77 photos of Pentagonite associated with Calcite | CaCO3 |
| 76 photos of Pentagonite associated with Stilbite-Ca | NaCa4(Si27Al9)O72 · 28H2O |
| 68 photos of Pentagonite associated with Mordenite | (Na2,Ca,K2)4(Al8Si40)O96 · 28H2O |
| 64 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 |
| 9 photos of Pentagonite associated with Heulandite-Ca | (Ca,Na)5(Si27Al9)O72 · 26H2O |
| 8 photos of Pentagonite associated with Apophyllite Group | AB4[Si8O20]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. | Hydroxyapophyllite-(NH4) | (NH4)Ca4(Si8O20)(OH)(H2O)8 |
| 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
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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
Showing 7 localities.
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