Cavansite

Cavansite is a striking hydrous calcium vanadium silicate prized by collectors for its intense, electric-blue color, a hue produced directly by its vanadium content. Chemically Ca(VO)Si4O10·4H2O, it crystallizes in the orthorhombic system as slender, radiating acicular crystals that build up into spherical rosettes and sprays rarely exceeding a centimeter across, often perched dramatically on contrasting white or colorless matrix. It is dimorphous with pentagonite, sharing an identical chemistry but differing subtly in crystal symmetry, making the two species notoriously difficult to distinguish without careful examination. With a hardness of only 3 to 4 and perfect cleavage, cavansite is delicate and rarely faceted, so it is collected almost exclusively as natural crystal specimens rather than cut gemstones.

The species was first described in 1973 from a discovery near the Owyhee Dam in Malheur County, Oregon, USA, which remains its official type locality, alongside the nearby Chapman quarry in Columbia County. There, cavansite forms as cavity fillings and veinlets in vesicular basalt and tuff breccia, in association with calcite, stilbite, and heulandite. Far more famous among collectors, however, are the basalt quarries of Wagholi, near Poona (Pune) in Maharashtra, India, part of the volcanic Deccan Traps. Indian material set the standard for the species, producing large, aesthetic sprays of deep blue cavansite balls draped over big crystals of white stilbite, frequently accompanied by pale yellow rhombohedral calcite, apophyllite, and babingtonite. Clusters of these rosettes can exceed 5 cm and are often sold as dramatic floater specimens.

Beyond its classic North American and Indian occurrences, cavansite has also been reported in smaller, more anecdotal finds from the Aranga quarry in New Zealand and from a municipal quarry in Rio Grande do Sul, Brazil, though these rarely rival the quality of the Wagholi or Owyhee material. Because good, gem-quality micromounts and thumbnail specimens are genuinely hard to find — especially the open, transparent radiating clusters nestled between larger stilbite crystals — fine cavansite commands strong interest among zeolite and secondary-mineral collectors worldwide. Its combination of true type-locality history, vivid saturated blue color unmatched by almost any other common mineral, and association with classic zeolite suites from Oregon and India make cavansite a benchmark species for basalt-hosted mineral collections.