| Cavansite | |
| Category: | Silicate mineral |
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| Formula: | Ca(VO)Si4O10·4(H2O) |
| Imasymbol: | Cav[1] |
| System: | Orthorhombic |
| Class: | Dipyramidal (mmm) H–M Symbol: (2/m 2/m 2/m) |
| Symmetry: | Pcmn |
| Unit Cell: | a = 9.792(2) Å, b = 13.644(3) Å, c = 9.629(2) Å; Z = 4 |
| Color: | Brilliant sky-blue to greenish blue |
| Habit: | Radiating acicular prismatic crystals commonly as spherulitic rosettes |
| Cleavage: | Good on |
| Tenacity: | Brittle |
| Mohs: | 3 - 4 |
| Luster: | Vitreous, pearly |
| Refractive: | nα = 1.542(2) nβ = 1.544(2) nγ = 1.551(2) |
| Opticalprop: | Biaxial (+) |
| 2V: | Measured: 52° |
| Birefringence: | δ = 0.009 |
| Pleochroism: | Visible: X=Z= colorless Y= blue |
| Streak: | Bluish-white |
| Gravity: | 2.25 - 2.33 |
| Diaphaneity: | Transparent |
| References: | [2] [3] [4] [5] |
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.
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.
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.