Unknown Amphibole - pyroxene

My unknown amphibole or pyroxene is from the Franconia Iron Mine, Sugar Hill, New Hampshire. It is fibrous, pale-green. Minerals on the same specimen include andradite garnet (EDS confirmed), quartz, and magnetite. A qualitative EDS analysis of this fibrous pale-green mineral indicated the presence of Si, Mg, Ca, O, Fe, and minor Al, (EDS plot below ).
The field of view for photo below is about 1 cm. Unknown mineral with red andradite garnet.
The field of view forsecond photo below is about 2 mm .
The EDS analyst suggested "a sub-calcic AUGITE pattern." None of the augite photos on mindat looks anything like this mineral. This material matches no previously reported species from this locality.
Looking for suggestions as to what this might be.

Tom Mortimer

Diopside

Hi Tom,

I like Rob's idea of Diopside. One might consider somewhere in the Diopside-Hedenbergite Series to account for the Fe but sure, closer to Diopside. The other Clinopyroxene that should be considered is Augite, since it does explain the others you have like Na that are common impurities in Augite. Rightly stated I think by your analyst when suggesting "sub-calcic", Ca does seem a bit low. BTW, I'm with you, it doesn't "look" like Augite, in fact to me it actually looks visually a bit like Actinolite (an Amphibole), which does have a similar looking spectra. Just my two cents, all the best.

Ron



Edited 1 time(s). Last edit at 11/09/2009 12:35AM by Ronald John Gyllenhammer.

Typical Actinolite. As we joking "Actinolite-(Ac)"... Brother of Neptunite-(Np) and chlorite-(Cl)

I would also suggest Actinolite as I have similar specimens from Arendal and Kragero, Norway.

Spencer.

O.K. I'll back off on the diopside. See if you can see any cleavage or believe the others, or x-ray it.

Rob, Ron, Spencer, & Pavel,
Thank you for your input. I think the Actinolite identification is the best fit. I looked closely at several specimens of this mineral with up to 60x magnification. The fibers are so fine that I was unable to distinguish any cleavage. Although more common elsewhere, actinolite is a rare species for New Hampshire. Several bladed structure amphiboles from other NH localities that I thought to be actinolite have been analyzed to be ferrohornblende.

Tom Mortimer



Edited 1 time(s). Last edit at 11/11/2009 01:27AM by Tom Mortimer.

Perhaps Tremolite.

Hello,

Actinolite most likely.

Not tremolite, as there is a Ca peak.

Regards,
Sebastian Möller

Hi Sebastian,

Actinolite and Tremolite both have Ca peaks, did you mean to say, "...there is an Fe peak" ? [www.cannonmicroprobe.com]

Ron

Hi Jon,

Sorry, yes, I meant a Fe peak. So this is either a Fe-rich tremolite (no pure endmember) or an actinolite.

Regards,
Sebastian Möller