Cavansite

Cavansite, named for its chemical composition of 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. Its 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
Category	Silicate mineral
Formula	Ca(VO)Si4O10·4(H2O)
IMA symbol	Cav[1]
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H–M Symbol: (2/m 2/m 2/m)
Space group	Pcmn
Unit cell	a = 9.792(2) Å, b = 13.644(3) Å, c = 9.629(2) Å; Z = 4
Identification
Color	Brilliant sky-blue to greenish blue
Crystal habit	Radiating acicular prismatic crystals commonly as spherulitic rosettes
Cleavage	Good on {010}
Tenacity	Brittle
Mohs scale hardness	3 - 4
Luster	Vitreous, pearly
Streak	Bluish-white
Diaphaneity	Transparent
Specific gravity	2.25 - 2.33
Optical properties	Biaxial (+)
Refractive index	nα = 1.542(2) nβ = 1.544(2) nγ = 1.551(2)
Birefringence	δ = 0.009
Pleochroism	Visible: X=Z= colorless Y= blue
2V angle	Measured: 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

• Members of the apophyllite group
• Members of the zeolite group, particularly stilbite
• babingtonite, Ca₂Fe₂Si₅O₁₄OH
• quartz, SiO₂
• calcite, CaCO₃
• pentagonite, Ca(VO)Si₄O₁₀ · 4(H₂O)

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.