FMF - Friends of Minerals Forum, discussion and message board

[Leon56]

I recently bought a mineral named as Pentagonite - Wagholi, Pune District (Poonah District), Maharashtra, India.
A colleague who is an expert on minerals told me that this was not Pentagonite but Cavansite - what is the difference? Do I really have a completely different mineral?

Photo my "Pentagonite" on Stylbite.

[Maxilos]

Hi,

I would say pentagonite. I did a quick search on google for pentagonite and on cavansite. Some of the pictures from pentagonite looked exactly like jours.

Mark

[Minex]

[Maxilos]

Hi,

It is a extremely cool mineral. I like the blue pentagonite with the white-gray stylbite on the background.

Mark

[Leon56]

Citation:

Some of the pictures from pentagonite looked exactly like jours.

Yes, of course. I bought this mineral in Web minerals shop and used their picture. I hope that this is not prohibited, because this mineral was sold to me.

[Tomasz Praszkier]

Leon,
this is pentagonite.
Tomek

[Leon56]

Tomasz,

How do you know? I think the difference in crystal structure, but I'm not sure

[Tomasz Praszkier]

If you speak German you can download one of my articles about cavaniste and pentagonite. There is described difference in details: https://mineralsandfossils.org/spiriferminerals/MW_6_2009_Cavansit_final.pdf
(link normalized by FMF)

Shortly - color is very light blue, crystals are well formed, gem, shape of cluster is typical for pentagonite.

Good luck!

[John S. White]

Pentagonite crystals are often twinned, in fact the name derives from twins that consist of five individuals, as you can clearly see on the small crystal at the right of this photo, it is a perfect five-pointed star.

[Tomasz Praszkier]

John,
whats interesting pentagonites from India are quite rare twinned - usually if they are formed as single crystals.

[John S. White]

I agree, most twins are but two crystal pairs. They are rare but if you spot one you know you have pentagonite and not cavansite.