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Monazite or ?

Posted by James Christopher  
James Christopher January 31, 2012 02:44AM

I got this at a locality that is not listed at all, a large cavity in Pikes Peak granite that mostly has extremely large quartz crystals. Hematite coatings are also present extensively, another unknown and much more radioactive mineral, and what we believe is columbite/tantalite.
This one has the color better shown in the first photo. The second shows the shape in general better. SG is 5.45, hardness 5.5-6. It is slightly radioactive, but nowhere near what the other unknown is(which I may post at a later time) Any guesses as to this one? It does seem transparent in the one uncoated brown section in the first photo.

Edited 1 time(s). Last edit at 01/31/2012 02:45AM by James Christopher.
open | download - unk REE.jpg (287.3 KB)
open | download - DSCF6065.jpg (153.9 KB)
Craig Mercer January 31, 2012 03:16AM
Hi James,

Definitely everything points to it being Monazite. Gadolinite one of the associates is quite similar, just a little harder.

Anyway goodluck mate,
James Christopher February 05, 2012 01:32AM
New twist, Raman is saying it's a carbonate, but it's too hard for Bastnäsite. Any other thoughts?
James Christopher February 05, 2012 05:46AM
Brian wrote: I can scratch with 6, but not with 5. So we can agree on 5 < H < 6. My crystals even have some flat and clean section of phases here and there. And I do not think that we have a situation here like with hematite where the high toughness makes it hard to scratch.

Literature for Bastnäsite: 4-4.5

That would rule it out.

But - all other attributes are right: color reddish brown luster waxy translucent uneven fracture tabular parting on 001, in that direction prismatic, hexagonal

Here is the Raman spectrum. The 1100 cm^-1 peak is carboate. When you compare with the RRUFF database note that there is wavelength and polarization dependence which determines the relative peak intensity.

In general, our spectrum is a very high good spectrum with narrow peak, and well defined modes. This indicates a well defined crystal.

This one comes close, just was acquired with lower resolution.

That would settle it if .... hardness ... and low radioactivity.

I read 20 g pieces have 14 kBq. My 20 g piece held to one side of crystal registers 20-30 cps. Let's make a first order estimate, I capture 1/6th then total would make <200 cps.
Rudy Bolona February 05, 2012 08:02PM
Hey Jim,
Is the entire specimen mono-mineralic? I found something very similar to this a couple of years ago In Pikes Peak granite and it still remains a mystery to me.
James Christopher February 06, 2012 01:12AM
Yes, it appears to be one mineral.
James Christopher February 15, 2012 06:50AM
open | download - IMG_20120214_190749.jpg (212.8 KB)
Ralph Bottrill February 15, 2012 10:49AM
It looks like a crichtonite group mineral?

James Christopher February 15, 2012 01:33PM
No Ti or Sr however. Is gadolinite with Sm instead of La possible? I also don't have 100% confidence in the XRF being used. I may send it somewhere for further testing

Edited 1 time(s). Last edit at 02/15/2012 01:37PM by James Christopher.
James Christopher February 24, 2012 11:34PM

Ok, a more trustworthy semiquantative XRF. Raman is going to be redone as it indicates a carbonate. Any new ideas?
open | download - Unk XRF.jpg (273.3 KB)
Rudy Bolona February 25, 2012 01:52AM
Hey Jim,

Did you find multiple specimens of this mineral?
James Christopher February 25, 2012 02:15AM
I believe so Rudy. Guess that's a hint huh? I'll see if I can get you one sometime assuming we find more. I am saving one for Dean, as he didn't get one yet, and he, Markus and I are the claim owners. Markus and I have one. Well, I have 2 (tu)
Pavel Kartashov February 25, 2012 07:51PM
James, I see photos of your mineral and see your analytical data. And I unable to believe, that the later are connected with the former.
I can't to imagine that your mineral from photo is gadolinite-(Ce) with 14 mas.% of Fe. There must be some misunderstanding. in any case it would be better to check P content instead of Ni, Co, Rb and Cs.

Edited 1 time(s). Last edit at 02/25/2012 07:55PM by Pavel Kartashov.
Ralph Bottrill February 25, 2012 09:47PM
Possibly biraite if the carbonate is confirmed?

Pavel Kartashov February 26, 2012 12:28AM
I am think, mixture (apo-gadolinite oxidized silicate glass with bastnasite) was analyzed.
What about biraite, I would be very surprised to found it in such situation. Besides that total REE content of the mineral is too low for biraite.
High Al and K+Na concentrations puzzling me. May be it is something completely new, if it isn't mixture? Here is very strange combination of fresh appearance of mineral and bad analyses typical for mixtures...:-S
James Christopher February 26, 2012 02:49PM
How deep do the x-rays penetrate? The one I had analyzed looked to be one mineral, but another I have may be one mineral about 1 mm thick over another. So maybe the first is as well. Maybe the inner is the carbonate, the outer the silicate? The inner still has a hardness>5 though. I think Markus is going to do single crystal xrd eventually on it
James Christopher March 12, 2012 04:40AM
After Markus sacrificed one to the saw, it appears the unknown is Monazite with a Bastnäsite outer coating. The Fe is probably from some scattered hematite, and I imagine they didn't xrf the cleanest side which I asked for, so the Si is probably from the feldspar, Al as well. The monazite interior explains the density greater than bastnäsite should have. Hardness is the only slightly off variable, but I bet there is an explanation for that as well. How common is this mineral combination?
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