Cavansite

Cavansite, whose name is derived from its chemical composition, calcium vanadium silicate, is a deep blue hydrous calcium vanadium phyllosilicate mineral, occurring as a secondary mineral in basaltic and andesitic rocks along with a variety of zeolite minerals. It's blue coloring comes from vanadium, a metal ion.[6] Discovered in 1967 in Malheur County, Oregon, cavansite is a relatively rare mineral. It is polymorphic with the even rarer mineral, pentagonite. It is most frequently found in Pune, India and in the Deccan Traps, a large igneous province.

Cavansite
Cavansite on heulandite
General
CategorySilicate mineral
Formula
(repeating unit)		Ca(VO)Si4O10·4(H2O)
IMA symbolCav[1]
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H–M Symbol: (2/m 2/m 2/m)
Space groupPcmn
Unit cella = 9.792(2) Å,
b = 13.644(3) Å,
c = 9.629(2) Å; Z = 4
Identification
ColorBrilliant sky-blue to greenish blue
Crystal habitRadiating acicular prismatic crystals commonly as spherulitic rosettes
CleavageGood on {010}
TenacityBrittle
Mohs scale hardness3 - 4
LusterVitreous, pearly
StreakBluish-white
DiaphaneityTransparent
Specific gravity2.25 - 2.33
Optical propertiesBiaxial (+)
Refractive indexnα = 1.542(2) nβ = 1.544(2) nγ = 1.551(2)
Birefringenceδ = 0.009
PleochroismVisible: X=Z= colorless Y= blue
2V angleMeasured: 52°
References[2][3][4][5]

Uses of cavansite

Although cavansite contains vanadium, and could thus be a possible ore source for the element, it is not generally considered an ore mineral. However, because of its rich color and relative rarity, cavansite is a sought-after collector's mineral.

Associated minerals

Notes for identification
Stalactitic cavansite, 3.6 x 2.1 x 1.8 cm, Wagholi, Pune District, Maharashtra, India

Cavansite is a distinctive mineral. It tends to form crystal aggregates, generally in the form of balls, up to a couple centimeters in size. Sometimes the balls are coarse enough to allow the individual crystals to be seen. Rarely, cavansite forms bowtie-shaped aggregates. The color of cavansite is distinctive, almost always a rich, bright blue. The color is the same as its dimorph, pentagonite, but the latter is generally much more spikey with bladed crystals. Finally, the associated minerals are useful for identification, as cavansite is frequently found sitting atop a matrix of zeolites or apophyllites.

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. Mineralienatlas
  3. Handbook of Mineralogy
  4. Mindat
  5. Cavansite Mineral Data, Mineralogy Database webmineral.com
  6. "Minerals Colored by Metal Ions". minerals.gps.caltech.edu. Retrieved 2023-02-28.
  • Mineral galleries
  • Evans, H.T. Jr., "The crystal structure of cavansite and pentagonite", American Mineralogist, Vol. 58, pg. 412–424, 1973.
  • Makki, M.F., "Collecting cavansite in the Wagholi quarry complex, Pune, Maharashtra, India", The Mineralogical Record, Vol. 36, No. 6, pg. 507–512, Nov-Dec 2005.
  • Staples, L.W., Evans, H.T. Jr., and Lindsay, J.R., "Cavansite and pentagonite, new dimorphous calcium vanadium silicate minerals from Oregon", American Mineralogist, Vol. 58, pg 405–411, 1973. http://www.minsocam.org/ammin/AM58/AM58_405.pdf

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