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Identity HelpNeed locality - fan-shaped microcline crystal aggregate

19th Sep 2016 23:12 UTCHarold Moritz 🌟 Expert

A very cool fan-shaped aggregate of sub-parallel microcline (or perhaps orthoclase) with some quartz cling-ons. The terms of some of the microclines are hoppered. Measures 9x7x2.5 cm. From an old collection, no data, but supposedly he collected in New York State and never bought anything. Though some pieces are from Conn. and others must have been bought. I think this may be from New Hampshire. Anyway, thoughts appreciated.

20th Sep 2016 11:27 UTCErik Vercammen Expert

looks a bit like some feldspar crystals from http://www.mindat.org/loc-3970.html

20th Sep 2016 14:44 UTCHarold Moritz 🌟 Expert

I took another close look at the crystals under a microscope, which I had not done since before it was cleaned (and it needed it!), and now I can see that the crystals are albite overgrowths, which show the characteristic polysynthetic twinning. There may be elongated K-spar underneath, which makes me think it is like these albite/microcline assemblages from the same place:

http://www.mindat.org/gallery.php?loc=3970&min=96

The dark matter is micaceous clove brown and a little waxy, looks like vermiculite, or fine-grained phlogopite.

Thanks Erik, it could be from NM. The original owner did make a fossil collecting trip to west-central Texas, so it could very well be from nearby Dona Anna Co.

20th Sep 2016 19:18 UTCMichael C. Michayluk

Albite, Orthoclase

Rock Springs Canyon, Organ Mining District, Organ Mountains, Doña Ana County, New Mexico, USA

I am by no means an expert, but in all of the albite/microcline specimens I have seen from the Organs, the albite is not a microscopic overgrowth, but large and blocky and epitaxial?.... like this .

That's not to say it couldn't be from there... hopefully one of the more experienced New Mexico collectors comments

20th Sep 2016 19:54 UTCAlfredo Petrov Manager

I saw a piece from Konso, Ethiopia, just like this at the Denver show. I'm not, of course, suggesting your piece came from Ethiopia, Harold, but I fear the habit occurs at enough places that it will be impossible to definitively decide on a locality.

20th Sep 2016 20:13 UTCHarold Moritz 🌟 Expert

The albite is not microscopic, it covers most of the piece, which is a hand specimen, just the twinning is microscopic, as is typical.

Michael, thanks, that specimen is in the gallery I linked to earlier, I can see where there might be others that fully cover the K-spar, leaving a hole at the top where they pass over the K-spar termination. The elongated K-spar is unusual.

Alfredo, true, but the original owner had mostly fairly common things from a limited number of places, all USA, so I suspect it should be from someplace well known, but from decades ago.

20th Sep 2016 20:49 UTCPeter Slootweg 🌟

I think Eric is right. I have a specimen from the Organs http://www.mindat.org/photo-375770.html and it too shows on clean side and the other with same little black specks as the specimen shown. I think the habit may be a bit unusual form there but the whole combination makes it, in my opinion, very likely form the mentioned locality. However, Afredo makes a very valid point. It is hard to be 100% sure with a mineral that is so common.

20th Sep 2016 21:00 UTCHarold Moritz 🌟 Expert

Thanks Peter, I just noticed the orthoclase gallery for that locality based on your photo.

http://www.mindat.org/gallery.php?loc=3970&min=3026

It does look promising, though yeah probably will never know for sure, but the piece was too nice to not try.

I think we can ask the original owner if that place sounds familiar or more about its potential origin.

20th Sep 2016 21:53 UTCMichael C. Michayluk

I see I misunderstood you and was looking at your specimen wrong, but I still don't see a striking similarity to the specimens in the Organs gallery or ones I have seen in person.

20th Sep 2016 22:11 UTCDon Saathoff Expert

I cannot agree with the Organ Mountains as the source of this specimen. I've seen probably a hundred specimens of these orthoclase/albite growths. All have been very disorderly parallel growth stacked xls. There are two opened pegmatites in Rock Springs Canyon, one on the NW wall and one lower on the SE wall The pegmatite on the NW wall produced these columns of parallel growth orthoclase with albite (this peg was affectionatly locally known as the "Stinky Hole" and produced many small apatites, titanites to palm size, small zircons, attractive smokey/orthoclase combos.....but I've never seen an orthoclase specimen with a radial growth pattern. Since the pegmatite has been worked by collectors for at least 50 to 75 years there is NO TELLING what it produced early on.

SO, with all this said, I doubt Rock Springs Canyon but who can know?

BTW, twinning tends to indicate orthoclase as opposed to microcline according to Dunham, 1934.

Don S.

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