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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.


Classification of Pentagonite

Approved
9.EA.55

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
14.14.2

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}
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

Chemical Properties of Pentagonite

IMA Formula:
CaV4+OSi4O10 · 4H2O
Elements listed in formula:

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.05CuprorivaiteCaCuSi4O10
9.EA.05GillespiteBaFe2+Si4O10
9.EA.05EffenbergeriteBaCuSi4O10
9.EA.05WesselsiteSrCuSi4O10
9.EA.10EkaniteCa2ThSi8O20
9.EA.15Fluorapophyllite-(K)KCa4Si8O20F · 8H2O
9.EA.15Hydroxyapophyllite-(K)KCa4Si8O20(OH,F) · 8H2O
9.EA.15Fluorapophyllite-(Na)NaCa4Si8O20F · 8H2O
9.EA.20MagadiiteNa2Si14O29 · 11H2O
9.EA.25DalyiteK2ZrSi6O15
9.EA.25DavaniteK2TiSi6O15
9.EA.30Sazhinite-(Ce)Na3CeSi6O15 · 2H2O
9.EA.30Sazhinite-(La)Na3LaSi6O15 · 2H2O
9.EA.35ArmstrongiteCaZrSi6O15 · 2H2O
9.EA.40OkeniteCa10Si18O46 · 18H2O
9.EA.45NekoiteCa3Si6O15 · 7H2O
9.EA.50CavansiteCaV4+OSi4O10 · 4H2O
9.EA.60PenkvilksiteNa4Ti2Si8O22 · 4H2O
9.EA.60TumchaiteNa2ZrSi4O11 · 2H2O
9.EA.65NabesiteNa2BeSi4O10 · 4H2O
9.EA.70AjoiteK3Cu202+Al3Si29O76(OH)16 · 8H2O
9.EA.75ZeravshaniteNa2Cs4Zr3Si18O45 · 2H2O
9.EA.80Bussyite-(Ce)(Na,H2O)6(Ce,REE)3Be5MnSi9(O,OH)30F4
9.EA.85PlumbophyllitePb2Si4O10 · H2O
14.14.1CavansiteCaV4+OSi4O10 · 4H2O
14.14.3GoldmaniteCa3V23+(SiO4)3
14.14.4HaradaiteSrV4+Si2O7
14.14.5SaneroiteNa2(Mn2+,Mn3+)10V5+Si11O34(OH)4
14.14.6ErlianiteFe42+Fe23+Si6O15(OH)8
14.14.7EulytineBi4(SiO4)3
14.14.8BismutoferriteFe23+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.

Internet Links for Pentagonite

mindat.org URL:
https://www.mindat.org/min-3152.html
Please feel free to link to this page.
Specimens:
The following Pentagonite specimens are currently listed for sale on minfind.com.

Localities for Pentagonite

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.
(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
 
  • 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 (TL)
 
  • Oregon
    • Malheur Co.
      • Lake Owyhee State Park
Amer.Min.(1973) 58, 405-411 and 412-424
Mineral and/or Locality  
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