Pentagonite

Pentagonite
General
CategorySilicate mineral
Formula
(repeating unit)		Ca(VO)Si4O10·4(H2O)
IMA symbolPtg[1]
Strunz classification9.EA.55
Crystal systemOrthorhombic
Crystal classPyramidal (mm2)
(same H-M symbol)
Space groupCcm21
Unit cella = 10.386(4) Å,
b = 14.046(7) Å,
c = 8.975(2) Å; Z = 4
Identification
ColorGreenish blue
Crystal habitPrismatic crystals, often as radiating clusters
TwinningMultiple twins producing a pseudo pentagonal symmetry
CleavageGood on {010}
TenacityBrittle
Mohs scale hardness3 - 4
LusterVitreous
DiaphaneityTransparent
Specific gravity2.33
Optical propertiesBiaxial (-)
Refractive indexnα = 1.533 nβ = 1.544 nγ = 1.547
Birefringenceδ = 0.014
PleochroismVisible: X=Z= colorless Y= blue
2V angleMeasured: 50°
References[2][3][4]

Pentagonite is a rare silicate mineral with formula Ca(VO)Si4O10·4(H2O). It was named for the unusual twinning called a fiveling with an apparent five-fold symmetry.[2] It is a dimorph of cavansite.

Pentagonite was first described in 1973 for an occurrence in Lake Owyhee State Park, Malheur County, Oregon.[3] It has also been reported from the Pune district of India. It occurs as fracture and cavity fillings in tuff and basalt. It occurs with cavansite, heulandite, stilbite, analcime, apophyllite and calcite.[2]

References

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c Handbook of Mineralogy
  3. ^ a b Mindat.org
  4. ^ Webmin
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