What's in a Name - Cavansite

Mineral Matters #722

Cavansite, that beautiful blue mineral known particularly from the Wagholi quarries in India, where it has been extracted for many years. However, the Type Locality is Owyhee Dam, Lake Owyhee State Park, Malheur County, Oregon, USA, where it is much less significant.

So where does its name come from?

Many minerals are named for a place, a person, a structure, or a chemical composition. Cavansite is the latter. Its formula is Ca(VO)Si₄O₁₀·4H₂O, and it is named for the calcium, vanadium and silicon: Ca(lcium)Van(adium)Si(licon)te. Perhaps it should have been cavansiite to avoid any confusion with sulphur! 😆

There is an interesting discussion on Mindat about how to distinguish cavansite from its dimorph, pentagonite, using perceived colour difference under strong bluish light or sunlight. Both species can be notoriously difficult to accurately capture in a photograph.

I checked the cavansite below, and a pentagonite, using a strong LED torch (I don’t know what the colour temperature is, other than it is a bright bluish white), and I do detect a distinct greenish colour for the cavansite, and a distinct blue for the pentagonite. However, going by the discussion, I think the jury is still out on that one.

Below: Cavansite, Stilbite-Ca, Wagholi Quarries, Wagholi, Pune District, Pune Division, Maharashtra, India. Width of view 14mm.