Colorado Pegmatite Mystery Mineral

I recently had a specimen analyzed, that I collected at a Colorado pegmatite. It was an SEM-EDS microprobe. After the test the analyst had no idea what it could be. He sent this information to my email about the results: Y=Sm>Ce=Nd=Th>>Gd=Ca>>Tm. Wondering if anyone out there has seen this result. I asked the analyst about wether he was able to determine if it was a phosphate or silicate. he informed me that these elements usually get lost in the peaks for yttrium. I obtained a specific gravity of 5.11 on a sample. I am leaning towards phosphate, since silicates are usually much less dense. Monazite comes to mind, but wouldn't Cerium be the highest peak? Possibly xenotime,, but what about that high samarium reading. Sm-dominant monazite or xenotime? Any guesses out there.

Cheers!

Rudy

Hi Rudy,

I almost feel silly commenting because identity here is a "pig in a poke", sight unseen. Regardless, the results from remote viewing on my crystal ball are in, here are some possibilties just for fun...

Candidates- Aeschynite(Y)?, Monazite-(Sm), Synchysite(Nd), Petersite(Y)

Maybe- Shabaite (Nd), but your result lists no U???, Schuilingite(Nd), but your result lists no Cu or Pb??

Ron



Edited 1 time(s). Last edit at 10/05/2009 01:17AM by Ronald John Gyllenhammer.

Hi Ron,

I am thinking maybe Monazite-(Sm). Heavy elements such as niobium, copper, and lead should have turned up in the test. There may be more than one phase happening here. It looks very much like a monazite, except more yellow. The hardness is around 5.5. The crystal outlines look monoclinic. The interesting thing about this specimen is that it occurred in a pod of finely crystallized lepidolite in contact with quartz and albite (cleavelandite). the specimen itself is a crystalline oval mass within this structure. I will take photos and post them soon. I also noticed that one of the two occurrences of Monazite-(Sm) is from the Annie Claim #3 in Manitoba, Canada. It also occurred with lepidolite. Hmmm...

Rudy

Hello,

If the Y content is right, this should be no monazite. Monazite usually prefers LREE like Ce, La, Nd, but not Y.

I think a proper micropobe WDX analysis or a mass spectroscopy (e.g ICP-MS) should be done. Then you will be able to find Si or P as well as the REE pattern of the mineral.

Maybe you have an oxide/hydroxide (O and H don't show up in most spectra (light elements)) such as pyrochlore.

Regards,
Sebastian Möller

Hi Sebastian,

I will get a WDX analysis done on a sample. I have someone in mind who can do it for me. He is as equally enthused in these rare earth pegmatite minerals as I am. This mineral might be something never described before. That would be exciting! I will keep Mindat posted on any future results.

Regards,

Rudy

HI Rudy,

Sebastian as usual, makes a very good point about the Y content. Further analysis will clear this up I should think. Pegmatites are exciting and you always seem to make them even more so Rudy, thanks for sharing this one. Good luck on the next analysis.

Ron

Hi Rudy!
Was equation given by you in mas.% or in at.%? If it is in mas.%, the mineral is Y-dominant. While Y is twice (at least) lighter then any another rare earth metal it very often predominate in at.% when its content in mas.% isn't too high. Remember stories with "Chukhrovites-(Ce)". Very often in gadolinites-hingganites from W. Mongolia 8-7 mas. % of Y₂O₃ give predomination in at. % against 20 and more mas.% of Ce₂O₃ or Nd₂O₃.

So your mineral should be xenotyme-(Y) if it is phosphate. By the way you quite able to check this fact by microchemical reaction with ammonium molybdate.

But if on ED spectra P peak is absent, it may be fluorcarbonate or fluoride. So it may be (Y,REE)(CO₃)F or (Y,REE)F₃. REE carbonates fizz in HCl or HNO₃. Fluorides don't dissolve in them (only in boiling H₂.SO₄).
Bastnasite-(Y) may to looks like as usual monazite/xenotyme.
Has your mineral any crystallographical shape?

Kind regards,
Pavel

By the way, your mineral may to turned out a mixture. Only yesterday I met apatite coloured by monazite inclusions in pinkish-orange colour.

Hi Pavel!

Nice to hear from you. No percentages were given in the analysis, only that basic composition that I presented in my initial post. I am confused with the first part of it, which says Y=Sm. What about this Sm? Can contents of both Y and Sm be equal? I placed a sample in HCL and no fizzing occurred even after boiling in the acid. I left the sample in the test tube for a couple of days and the piece turned white. Also, I placed a sample over a blow torch flame. The mineral glowed and began to decrepitate at a steady rate. It did not fuse. Other monazites and xenotimes I have performed this test on have not decrepitated, and simply remained unfused and turned gray. It certainly could be a mixture of phases. The association of lepidolite is unusual in my experience with these species. I collected the specimen at the Brown Derby No. 1 pegmatite, Gunnison County, Colorado. A famous and well studied pegmatite. Seems odd that the past great mineralogists who did the work on this mine missed this one. it was pretty obvious on the lepidolite pod. I am including some photos of samples. Notice lepidolite association. the largest piece is 6 cm across.

Best Regards,

Some close ups.

One more just for fun

Hi Rudy,

I can see why you think Monazite (Sm), although the yellow is a little troubling, perhaps another species intergrown, like Pavel said maybe Xenotime . My ref. specimen of monazite from Brown Derby is very similar, as I recall.

Ron

I never saw lepidolite in association with K-feldspar of such colour! It is very interesting!

Look at [www.mindat.org] May be you really have YF₃?

By the way, interesting feature of this fluocerite from Katugin - it give PXRD pattern identical to thorianite one. I was VERY surprised.

Pavel,

The dark red material is the mineral in question. As far as the bright yellow mineral, Well, that's another can of worms. Only white cleavelandite in association.

Hey Rudy,

That's a big ugly crystal .

I always thought that the Lanthanides (Sm,Ce, Nd here) behaved the same such that you cannot distinguish them chemically.

With the lepidolite/albite association, you may want to search the Pala, Harding and appropriate Norway localities for the top contenders.

Did you find it next to the mine shack, inside the main adit, or west of the gated area?

-Dean Allum

Hi Dean,

I found this one on a lepidolite pod in the decline, which is just north of the largest gated adit. This entrance also has the fence. This mine now looks to be abandoned by the people who were working it. All chains and locks have been cut by who knows who. The decline is a little spooky to be in. The ceiling has been shored up by logs. While I was hammering this thing out I was thinking about those stories of sudden cave-ins. Take a lantern and headlight if you go. Be careful where you step. A very neat pegmatite with lots going on. As far as coming out with a world class specimen; I don't think so. No large mariolitic cavities. Everything is embedded in tough matrix. One of my Colorado pegmatite dreams is to find some new indescribed species. Hoping this might be one. By all appearances this looks to be some sort of monazite or xenotime transmogrified creature. Not much left of the Colorado collecting season. Get your skis ready!

Good Luck!

Unless you used more than one analyst, I was there the night your sample was analysed, but left before it was done. The =, <. > all refer to the EDS peak heights. Without WDS nothing can be said about atomic or weight %. Of course the exception is when you have an EDS of known composition and your unknown pattern with the same scale taken at same current and voltage matches exactly. Then you only have to worry about polymorphs!!!
Good luck with it.

Hi Rob,

Thanks for clarifying the = and >. I thought they may have been percentages. Do you guys perform WDS there? Is the sample still there?

The answer is yes to WDS when a window is fixed and it may well be done by now. If not then in a day or so. I'll alert the analyst to this thread, but I'll bet money that your sample is still there. He seems to always keep things though he'll return things if people ask, but they seldom do.

Thanks Rob! Have him contact me about compensation for the WDS analysis.

Hi Rudy,

One of the rules of thumb I've relied on from time to time is that a monazite without a phosphorus peak is a bastnaesite. I can only refer to the monazite-ce crystals I've found in Texas, but the phosphorus peak is usually going to be big enough to keep it from being hidden beneath yttrium lines. I have several spectra that I can post for comparison purposes. Can you post your spectrum? Are the peaks identified in it?

One statement caught my attention. The specimen turned white when exposed to acid. Monazites are phosphates which are acid labile. An overnight soak in 31% HCl will turn one of my monazites into a dense radioactive white fibrous mass. Another test for mineral phosphates is the magnesium thermite test. A small sample of the suspected phosphate is crushed, mixed with powdered magnesium and ignited. If you have a phosphate, the reaction mixture will flare up leaving a puddle of char mixed with bits of reduced REE metal. You'll also end up with pure molten thorium which will proceed to ignite in the air. I don't recommend it as the smoke may well be radioactive. BTW, this is one method by which monazite is smelted for thorium and LREE's.

I have quite a lot of credit on file with the University of Oklahoma Microprobe lab. If you can get me a small chip of the mineral, no bigger than 1/8", I'd be happy to submit it to George Morgan for analysis. His machine ID's peaks and generates guesstimated elemental percentages, although I usually just compare peak heights for ID purposes.

Good luck on your find. Here's hoping it's new. If I can find it, I'll post the spectrum and photo of one that I think may be a new mineral.

Frank