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.
Dimorph of:
Structurally related to plumbophyllite.
Ishida et al. (2009) suggest that cavansite is a low-temperature form and pentagonite a high-temperature form.
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.
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
GUID
(UUID V4):
(UUID V4):
a2613940-d664-4f08-99ec-dee3b0fd6629
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
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
and does not take into account mineral colouration.
Surface Relief:
Low
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
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.
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
Remove metal-metal sticks
Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
Remove metal-metal sticks
Display Options
Black Background | White Background
Perspective On | Perspective Off
2D | Stereo | Red-Blue | Red-Cyan
Black Background | White Background
Perspective On | Perspective Off
2D | Stereo | Red-Blue | Red-Cyan
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
Console Off | On | Grey | Yellow
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-𝑇 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:
Reference:
Staples, L.W., Evans, H.T., Jr., Lindsay, J.R. (1973): Cavansite and pentagonite, new dimorphous calcium vanadium silicate minerals from Oregon. American Mineralogist: 58: 405-411.
Synonyms of Pentagonite
Other Language Names for Pentagonite
Common Associates
Associated Minerals Based on Photo Data:
82 photos of Pentagonite associated with Heulandite Subgroup | (Na/Ca/K)5-6[Al8-9 Si27-28 O72] · nH2O |
73 photos of Pentagonite associated with Calcite | CaCO3 |
70 photos of Pentagonite associated with Stilbite-Ca | NaCa4(Si27Al9)O72 · 28H2O |
65 photos of Pentagonite associated with Mordenite | (Na2,Ca,K2)4(Al8Si40)O96 · 28H2O |
54 photos of Pentagonite associated with Stilbite Subgroup | M6-7[Al8-9Si27-28O72] · nH2O |
17 photos of Pentagonite associated with Cavansite | Ca(VO)Si4O10 · 4H2O |
9 photos of Pentagonite associated with Quartz | SiO2 |
5 photos of Pentagonite associated with Basalt | |
5 photos of Pentagonite associated with Gyrolite | NaCa16Si23AlO60(OH)8 · 14H2O |
3 photos of Pentagonite associated with Heulandite-Ca | (Ca,Na)5(Si27Al9)O72 · 26H2O |
Related Minerals - Strunz-mindat Grouping
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. | Hydroxymcglassonite-(K) | KSr4Si8O20(OH) · 8H2O |
9.EA.05 | Cuprorivaite | CaCuSi4O10 |
9.EA.05 | Gillespite | BaFe2+Si4O10 |
9.EA.05 | Effenbergerite | BaCuSi4O10 |
9.EA.05 | Wesselsite | SrCuSi4O10 |
9.EA.07 | Fluorapophyllite-(Cs) | CsCa4(Si8O20)F · 8H2O |
9.EA.10 | Ekanite | Ca2ThSi8O20 |
9.EA.15 | Fluorapophyllite-(K) | KCa4(Si8O20)(F,OH) · 8H2O |
9.EA.15 | Hydroxyapophyllite-(K) | KCa4(Si8O20)(OH,F) · 8H2O |
9.EA.15 | Fluorapophyllite-(Na) | NaCa4(Si8O20)F · 8H2O |
9.EA.20 | Magadiite | Na2Si14O29 · 11H2O |
9.EA.25 | Dalyite | K2ZrSi6O15 |
9.EA.25 | Davanite | K2TiSi6O15 |
9.EA.30 | Sazhinite-(Ce) | Na2CeSi6O14 · 6H2O |
9.EA.30 | Sazhinite-(La) | Na3La[Si6O15] · 2H2O |
9.EA.35 | Armstrongite | CaZr[Si6O15] · 3H2O |
9.EA.40 | Okenite | Ca10Si18O46 · 18H2O |
9.EA.45 | Nekoite | Ca3Si6O15 · 7H2O |
9.EA.45 | Perettiite-(Y) | Y2Mn4FeSi2B8O24 |
9.EA.45 | Badakhshanite-(Y) | Y2Mn4Al(Si2B7BeO24) |
9.EA.47 | Shlykovite | KCa[Si4O9(OH)] · 3H2O |
9.EA.50 | Cavansite | Ca(VO)Si4O10 · 4H2O |
9.EA.50 | Diegogattaite | Na2CaCu2Si8O20 · H2O |
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
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
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).
Struck out - Mineral was erroneously reported from this locality.
Faded * - Never found at this locality but inferred to have existed at some point in the past (e.g. from pseudomorphs).
All localities listed without proper references should be considered as questionable.
All localities listed without proper references should be considered as questionable.
India | |
| Praszkier et al. (2007) |
| Praszkier (2009) |
Praszkier (2009) | |
www.irocks.com (2002) | |
New Zealand | |
| Collection of RJ Martin |
USA (TL) | |
| Staples et al. (1973) +1 other reference |
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Wagholi Quarries, Wagholi, Pune District, Pune Division, Maharashtra, India