Mineral Mondays #5: Pentagonite

Pentagonite

Pentagonite is a rare silicate mineral sought after by collectors. While it is widely known amongst mineral collectors & dealers, it is not known to the average person.

Pentagonite is an interesting mineral. It is a dimorph of another mineral called cavansite. A dimorph in crystallography is a crystal with the same chemical structure, but it crystalizes differently. Pentagonite & Cavansite have the same chemical make up, but they differ in their crystal structure. Pentagonite forms in five pointed, long crystals while cavansite forms in ball shaped clusters.

Some Pentagonite Facts:

Pentagonite is a dimorph of cavansite.
Shape - orthorhombic
Composition - calcium, vanadium, silicate
Hardness - 3 - 4 (low, diamond is 10)
Refractive index (fire) - 1.54 (diamond is 2.417 - 2.419)

What attracted me to pentagonite was it's electric blue color. It's so stunning you have to stop and ask what it is. Add to that it is rare. Originally discovered in Oregon, I have never seen a specimen from there, it was only mined in any quantity in India from one mine. That mine that produced it has been closed so there will be no more new material on the market. Kinda like crypto, once it's mined it's done.

Enjoy some additional photos of pentagonite.