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Identity HelpUnknown purple stuff from gaspéite TL

13th Jun 2014 00:36 UTCJamie Cheshire

Would anyone like to take a shot at identifying the purple material on this piece? It hails from the gaspéite type locality:

http://www.mindat.org/loc-179457.html

The matrix is a big hunk of pea-green gaspéite. The purple has the same texture as the gaspéite, and the color suggests chromium content. What do you think?

James

13th Jun 2014 14:41 UTCChristian Auer 🌟 Expert

A wild guess because I don`t know the locality (although it seems ultramafic):

Kämmererite http://www.mindat.org/min-2149.html

13th Jun 2014 16:01 UTCReiner Mielke Expert

Although Cr bearing minerals have never been documented from there it is possible that it might be kammererite. Would be worth sending a piece off for analysis. I'd like to get a small (1.5-2cm) piece for my collection as I have nothing like it from there, if you send me one I will get it analyzed.

13th Jun 2014 20:05 UTCMark Heintzelman 🌟 Expert

The noted lack of both Chromite and any Chlorite minerals for this locality does cast some doubt on this suggestion. Where there's kammererite, there are also zones with straight-up Clinoclore, i.e. "Pennite" as well. But yes, Chromite and Chlorite Minerals are associates at several of the other the Gaspeiite localities . . . it is certainly a possibility that both are present, but relatively uncommon at this locality. Chromite also colors Serpentine in the same way, so with close examination it should be obvious if it is micacious (kammererite), or not (serpentine).

Just to play devils advocate here, Annabergite is noted as present at this locality, so why not it's cobalt analogue Erythrite is as well? Anecdotally, there seems to be a fair regional presence for Cobalt as opposed to Chromium, but I too am unfamiliar with the regional geology, so note of that may be entirely unrelated to this issue.

MRH

14th Jun 2014 01:07 UTCJamie Cheshire

Chromite does occur here. From the original gaspéite description, page 678: "Enclosed in the magnesian

gaspeite are a small amount of serpentine and a (Cr, Al) spinel (5 to 10% and less than 5%, respectively)."

I've only looked at the material with a hand lens, so I can't say for sure if it's micaceous or not. I'll get it under a dissecting microscope asap. I will also try to loosen a few crumbs for EDS.

Thanks for the feedback, y'all.

James

14th Jun 2014 01:30 UTCReiner Mielke Expert

Yes there is serpentine there and spinel as I have samples of both, however I wasn't aware of any significant Cr content in the spinel. They didn't present any analysis to back up their conclusion. It also raises the question as to whether or not it is magnesiochromite rather than spinel. Unless someone has an analysis available I will send a crystal off for analysis. However all I have ever seen is green serpentine, never purple. Going with the Cr idea it could also be stichtite rather than kammererite. As for erythrite, that is a secondary mineral and I have never seen any primary cobalt minerals only Ni ones so to me that seems unlikely, but not impossible.

14th Jun 2014 01:50 UTCReiner Mielke Expert

Hello Mark,

"Chromite also colors Serpentine in the same way" do you have a reference for this? I've looked at hundreds of chromite samples in serpentinite (from our chromite deposit http://www.mindat.org/loc-254288.html) but have never seen purple serpentine, although I have seen kammererite with the chromite. On the other hand maybe I'm just not recognizing the purple serpentine thinking it is kammererite ( thought it was stichtite at first but analysis showed it was kammererite).

14th Jun 2014 13:42 UTCMark Heintzelman 🌟 Expert

Reiner,

As I noted, I am not familiar with this particular locality, the suggestion is a general observation and characterization of the effect Chromium can have also on the coloration of various serpentine group minerals. It can be observed at multiple sites all along the state line chrome district in Maryland and Pennsylvania. I also agree that Stichite is a good possibility.

The serpentine deposits along Staten Island NYC are not particularly rich in Cr either (albeit, far more than just "trace at best"), and they have been studied and collected from at various sites for a very long time. Only recently (2006) were both Stichite and Chromium clinochlore observed in specimens from that general locale (specifically at the Todt Hill site). Unexpected yes, but definitely confirmed. You never know. :D

http://www.mindat.org/photo-142548.html

http://www.mindat.org/photo-14898.html

http://www.mindat.org/photo-612983.html

Review the data Jeff has provided with this last image, and it may give you some insight on just how complicated confirming an I.D. may be.

http://www.mindat.org/photo-143568.html

14th Jun 2014 20:36 UTCVandall Thomas King Manager

Why isn't the pink matrix the "variegated silicious dolomite"?

15th Jun 2014 01:40 UTCReiner Mielke Expert

From what I have seen the dolomite from there is yellowish to buff.

Thanks Mark! I will have to pay closer attention to the purple stuff from our deposit, some may be purple serpentine rather than kammererite, although both are relatively rare despite all the chromite around.

16th Jun 2014 22:58 UTCVandall Thomas King Manager

Have you made a scratch test? Does it fizz in acid?

17th Jun 2014 11:06 UTCAlfredo Petrov Manager

As annabergite/erythrite has been mentioned, remember that it takes only a minor amount of Co to make annabergite pink instead of green - So pink annabergite might be more likely than the as-yet-unreported erythrite.

In any isomorphous series where the end-members are of different colours, one cannot expect the colour to conveniently switch at the mineralogical 50:50 boundary.

(Note that I'm not suggesting the pink material is annabergite, just pointing out that colour is not a good indicator of erythrite in this case.)

17th Jun 2014 13:26 UTCVandall Thomas King Manager

I would add that annabergite-erythrite is not a matrix-forming mineral. It occurs on post-mine surfaces as well as in vugs. To be sure, annabergite-erythrite may fill vugs, but it would still have no paragenetic resemblance to the fine-grained pink matrix shown. Without even a simple hardness test to show for it, I would bet five cents that the pink matrix shown contains dolomite.

17th Jun 2014 23:37 UTCMark Heintzelman 🌟 Expert

Thanks for the insight and Better understanding of Annebergite/Erythrite Alfredo, much appreciated.

I did however assume from the photo that perhaps the purple was simply staining or in-filled fissure . . not a matrix forming mineral. Not the best example mind you, but Erythrite fills seams and even appears to color the calcite at this venerable old locale http://www.mindat.org/photo-14902.html . The origin is the Co is the local Pyrite, although Coballtite in micro xtls are present there as well. Admittedly a wild suggestion at best, but given the (seemingly changeable) opinion that Cr is not noted at this locality. . .

I am hoping to hear what it "actually" is . . still pretty curious. Thanks all for keeping this tread fairly active

MRH

18th Jun 2014 03:43 UTCVandall Thomas King Manager

"Science is a wonderful thing. Nowhere else can you get such a wholesale amount of conjecture from a trifling investment of fact" - Mark Twain. Instead of trolling Mindat for look-alike photos, we first need to know something about the physical properties of the actual sample. The chemical analysis of the vein material itself was very low in Cobalt. The pink matrix is visibly granular, not earthy or fibrous. What does a scratch do? What is the color of the powder? What happens when some pink fragments are put into acid? Why does the pink matrix maintain its coherence next to the weathered surface? Does the owner have some dense liquids to do a sink-float test. If the mineral is suspected to have Co, has a borax bead test been done? Does the owner have a copy of Orsino Smith's book on qualitative analysis? The answer to some of these questions might be able to rule out dead end conjectures. Let the testing begin.

18th Jun 2014 05:16 UTCMark Heintzelman 🌟 Expert

Van,

You're quite right. Orsino Smith's book is right here on my shelf, but did I even crack it open to look and consider offering a suggestion for an "at home" test . . . no.

I am glad to hear from you "in particular" that it's recommended. I've decided I will make it one of my summer reads this year, and no longer just little used reference.

Thank you.

18th Jun 2014 11:47 UTCVandall Thomas King Manager

Awesome!

29th Jun 2014 02:30 UTCReiner Mielke Expert

Looks like it could be purple serpentine the black "spinel" from there is chromite not magnesiochromite, not enough Mg. Attached is the EDS of a crystal I had analyzed.

29th Jun 2014 05:55 UTCRalph S Bottrill 🌟 Manager

A quick search on Mindat failed to show any purple serpentine, and from decades looking at serpentines mostly loaded with chromite-magnesiochromite, stichtite etc I have not seen one either. It looks quite siliceous or cherty to me, rather than the waxy to earthy or micaceous look of stichtite, erythrite or kammererite, but I cannot believe we have not seen even a simple hardness test yet! Looking at the type location, it's described as a vein in siliceous varicolored dolomite. Another possibility is diopside which can be this colour.

2nd Jul 2014 04:46 UTCJamie Cheshire

I've managed to extract (with some difficulty) two grains of the purple material. I'm rather preoccupied at the moment, so it may be a while before I get an EDS analysis on it.

James

4th Jul 2014 17:40 UTCReiner Mielke Expert

Ralph,

See Mark's post. example he gave is : http://www.mindat.org/photo-14898.html

4th Jul 2014 23:53 UTCRalph S Bottrill 🌟 Manager

Thanks Reiner, missed that, but does anyone know if any modern research has been undertaken into ths material?

I understood than in kammererite the Cr replaces Al, but most antigorite is very poor in Al, so it's strange. It does look to be a mixture.

5th Jul 2014 04:53 UTCMark Heintzelman 🌟 Expert

Yes Ralph, it is very much intermixed material,

Another link to a pic I also offered as an example in that post, which gives a reference and a more detailed breakdown of this particular material (from a more recent examination). http://www.mindat.org/photo-143568.html The purple coloration in the serpentine in this region is also present in some of the massive fine grained material as well, and often enough is directly associated with, or rather grading to, more typical green serpentine. Whether that too is simply intermixed material . . . ?

As far as the serpentine deposits that I'm most familiar with goes, a good deal of it is borderline/polytype and/or intermixed with associated minerals, so a thorough exam in the lab is warranted if one wants to know, with any real certainty, exactly what they have. Little wonder why, at least locally, there is still in use so much "non-species", eye determinable nomenclature for the various serpentine "types".

MRH

6th Jul 2014 13:40 UTCRalph S Bottrill 🌟 Manager

Thanks Mark I missed your earlier links but this is all really interesting. The purple serpentine is obviously a complex mixture. I have done some work on stichtite and chromites and this is useful info. Stichtite varies from a pale pink to dark mauve and purple, partly due to Al/Fe/Cr variations but also the darker material can be finely intergrown with an odd purplish coloured mineral. This has a composition and XRD pattern that doesn't quite fit serpentine or chlorite but its quite Cr-rich, so dozyite may just fit. The trouble is that these assemblages are always fine grained, complex mixtures.

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