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Identity HelpTitanite, Microlite, Monazite?

18th Feb 2020 22:03 GMTJobe Giles

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Ian Nicastro and I have been around and around about these. Not as much looking for ID as much as just sharing and spitballing, I’ve already come to the conclusion that these will Not be effectively ID’d without analysis. The split crystal growth looks very similar to Titanite and titanite is found in the area. So is zircon, and other pegmatite hosted minerals. The little red crystals grow with Muscovite on Albite, typically on the lower portions of the pockets. Quartz diorite/monzonite pegmatite. 

18th Feb 2020 22:04 GMTJobe Giles

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Her with the split growth form

18th Feb 2020 22:05 GMTJobe Giles

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Another angle showing the parallel split growth.

18th Feb 2020 22:06 GMTJobe Giles

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Looking straight down from the top.

18th Feb 2020 22:07 GMTJobe Giles

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I love the color of these.

18th Feb 2020 22:09 GMTJobe Giles

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Another, different than the one above. Not sure what the other submetallic minerals are to the left. Probably columbite which has also been found. 

18th Feb 2020 22:16 GMTJobe Giles

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Another that’s laying on its side and exhibits some iridescence.

18th Feb 2020 22:18 GMTJobe Giles

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Same as the above crystal, showing the iridescence. 

18th Feb 2020 22:22 GMTJobe Giles

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These I believe might be a totally different mineral, but they are from the same plates as the minerals shown above. These are Bipyramidal. 

18th Feb 2020 22:23 GMTJobe Giles

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These have a slightly more yellow hue. 

18th Feb 2020 22:25 GMTJobe Giles

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These are in a recess in the plate, this makes it very difficult to photograph.

18th Feb 2020 22:25 GMTJobe Giles

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Monazite maybe...

18th Feb 2020 22:29 GMTJobe Giles

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Another of what I think are titanite. 

18th Feb 2020 22:29 GMTJobe Giles

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A bigger one. 

18th Feb 2020 22:31 GMTJobe Giles

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Looking at the crystal above end on. Interestingly... All of the crystals with this habit have the same fracture down the middle. 

18th Feb 2020 22:33 GMTJobe Giles

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And the last, another one that I’m not sure is one, this one never had the chance to grow. Haha

19th Feb 2020 14:37 GMTHarold Moritz Expert

It would help to know the overall mineralogy of the pegmatite. Is it fairly "simple", that is, the basic rock forming minerals with mica and maybe a little schorl and beryl; is it phosphate rich - with lithiophilite/triphylite pods and their secondaries; is it Li rich - with spodumene, elbaite, montebrasite, etc.; or Nb/Ta rich with col-tan, microlite, wodginite, tapiolite, etc.?
Whatever they are there is a near perfect cleavage perpendicular to what looks to be the long axis. And the symmetry looks orthorhombic, these characteristics strongly suggest topaz.

Titanite is not typical of pegmatites. Monazite-(Ce) is typical but cleavage is wrong (as it is for titanite) but mindat page for monazite-(Ce) says a parting is
"well-marked frequently present on {001}"
which could be what I see in the images.
Another maybe is hydroxylherderite, but these are typical of phosphate rich pegs and I would expect to see other secondary phosphates. And the cleavage and symmetry are also wrong. But it can be tough to tell from photos.

19th Feb 2020 20:26 GMTA. Mathauser

Don't forget garnet group too.

20th Feb 2020 02:22 GMTJobe Giles

Hi Harold, yes the pegmatite is fairly simple, lithium has only been found in the area in trace amounts, same with beryllium, many of the samples tested showed none. That’s not to completely rule it out since, to my knowledge) this specific occurrence has not been tested. So far, here is a list of confirmed minerals we have found: As far as Quartz is concerned, we have found hyaline, smoky, Onegite, Citrine, smoky Citrine, ametrine, and amethyst. Epidote, laumontite, Chlorite, Blue to green Albite, euhedral Schorl, goethite, some form of pyrite, columbite, red rutile, and zircon. I may be missing a couple others but those are the main ones off the top of my head. In answer to the suggestion below, so far I have not seen any garnet. Titanite and zircon are well documented to occur in the areas that have been studied that are within the area and that share the same granitic chemistry. This being a fringe pegmatite could possibly lead to some weird geology. But i don’t honestly know enough to say with certainty. Does this answer any of the vagaries of my original posting?

20th Feb 2020 02:32 GMTKeith Compton Manager

Location still unknown !

20th Feb 2020 04:28 GMTJobe Giles

Northern Sierra Nevada mountains in Northern California.

20th Feb 2020 13:00 GMTHarold Moritz Expert

I'm not an expert in that area, and when you get down into microcrystals and pegs, all sortsa interesting or rare things can happen. So I went through my pegmatite books, and I still like topaz, the cleavage and crystal form seems right. They all appear too flat to be garnet, sure if you had only one it could be a distorted garnet, but unlikely many would be distorted in the same way. But the perfect cleavage of topaz is a very likely indicator.

But photos 9 through 12 look like another mineral, different form and color than the others, could be zircon or xenotime-(Y)?

20th Feb 2020 16:50 GMTJobe Giles

That’s a really interesting thought, I had not even considered topaz. Although, I have been searching for it avidly hoping it would show up, so far we have not found any fluorite either. Although, I did find a quartz chunk that had purple spots in it that I wondered if it could be purple fluorite. I lost the rock and have not been able to locate it since. But I have not ruled out fluorite presence being a possibility (In relation to what type of pegmatite classification this could be, the presence of fluorite would narrow down the options). These little crystals tend to form in association with plentiful muscovite, some of the plates have hundreds of these flattened red crystals but very very small, even under 30x magnification it’s hard to make out their shape.

20th Feb 2020 23:44 GMTJohan Kjellman Expert

I think what you have may quite possibly be monazite, of which twinning is not unheard (compare Goldschmidt), the colour is also right. 
Images 9-12 may be xenotime or zircon, provided they are square bipyramids.
The association is also right for these minerals.

cheers

21st Feb 2020 00:53 GMTJohannes Swarts

Agree with Johan - my money is on monazite for the red-brown crystals, zircon or xenotime for the transparent yellow crystals.  Know anyone with a spectroscope?  Can be attached to a microscope ocular and will show REE lines in absorption spectrum.

I highly doubt topaz for the red-brown crystals - they do not appear to be orthorhombic.

21st Feb 2020 02:55 GMTJobe Giles

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Interesting thoughts! Here are some more images I took today.

21st Feb 2020 02:55 GMTJobe Giles

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And another 

21st Feb 2020 02:56 GMTJobe Giles

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21st Feb 2020 02:56 GMTJobe Giles

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21st Feb 2020 03:30 GMTJobe Giles

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I hope these angles help exhibit the crystal habit. Would it be possible for so many of the crystals to exhibit the same twinned habit? I’m certainly inclined to believe there are two minerals.

21st Feb 2020 03:32 GMTJobe Giles

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21st Feb 2020 04:06 GMTFrank K. Mazdab Manager

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here are a selection of monazite twin from Goldschmidt's Atlas of Crystal Forms.  The color, form(s), occurrence, all seem consistent with monazite.

21st Feb 2020 04:53 GMTJobe Giles

Wow Frank! That’s really helpful and seems to fit very well. 

21st Feb 2020 05:03 GMTFrank K. Mazdab Manager

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some additional twins and single crystals of monazite...

21st Feb 2020 18:12 GMTJobe Giles

I would be really curious to see how these compare to Titanite. I will spend some time going through the geological papers I have that discuss sampling and exploration of the area and see what there is as far as mentions of specific minerals. 

21st Feb 2020 03:34 GMTJobe Giles

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21st Feb 2020 03:35 GMTJobe Giles

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21st Feb 2020 14:07 GMTHarold Moritz Expert

Looks good, but you should still get them analyzed to really know, or it will haunt you (I know from experience!).

21st Feb 2020 15:20 GMTJobe Giles

Boy isn’t that the truth! It already does, I obviously obsess about it already, ever since I got a new and stronger loupe and a tripod for my iPhone I’ve been having fun getting some better shots of the crystallography. Maybe I’ll sell a couple to pay for the analysis.

21st Feb 2020 15:25 GMTJobe Giles

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This is the largest plate from the pocket and it’s the one that has the octahedral crystals. 

21st Feb 2020 15:33 GMTJobe Giles

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This little plate has many of the flattened crystals. Many of them are too small to see in the photo. 

21st Feb 2020 15:36 GMTJobe Giles

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This plate has the most of the flattened red crystals, there are literally hundreds of them tucked in the Muscovite and between the Albite. 

21st Feb 2020 19:40 GMTUwe Kolitsch Manager

A very simple and cheap method to distinguish between monazite and titanite is checking the colour under a tanning lamp (sunlamp).
Any REE mineral containing some Nd will show a greenish (not much Nd) to bluish (much Nd) colour.

Zappel, A. & Weiss, W. (1982): Zur Farbveränderung von Mineralien der Seltenen Erden unter der Höhensonne. Aufschluss, 33, 7-12 (in German).

Gorobets, B. S.; Rogozhin, A. A.; Ryabenko, S. V. (1989): Determination of rare-earth minerals under unfiltered light from a mercury lamp. USSR. Mineral. Zh. 11, 55-57. (in Russian)


22nd Feb 2020 00:44 GMTJobe Giles

That is such a cool suggestion! Thank you, I now have to go get a tan... taking a sack of rocks with me.

25th Feb 2020 07:12 GMTIan Nicastro

Great point Uwe, I hadn't thought of that! Jobe, my lizard's mercury vapor light will cause the Nd3+ color shift to greenish. If you can't find something up there to use feel free to send me a sample and I can test and send back. I still personally think we are dealing with  at least 2 different minerals here though. Sadly I've found most REE containing minerals I've sent for analysis are not easily resolved with just Raman. 

26th Feb 2020 05:32 GMTJobe Giles

Thank you Ian, your input is always highly appreciated and thank you for the offer! 

25th Feb 2020 01:24 GMTJobe Giles

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I found another mineral on these plates. The photo quality is terrible and tomorrow I will get better images. I’m thinking maybe allunite. This would have been included in the smoky quartz crystal but it broke right along the inclusions.

25th Feb 2020 01:26 GMTJobe Giles

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I’ve not seen these as inclusions in quartz before. Both images are under 20x magnification.

25th Feb 2020 01:30 GMTJobe Giles

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The white arrow points to the broken crystal where the mineral above is held. 

25th Feb 2020 12:29 GMTHarold Moritz Expert

Could be topaz again, transparent, (allanite is essentially opaque) looks orthorhombic. The whole nice pocket assemblage, relatively simple mineralogy, looks like a friendly place for topaz.

26th Feb 2020 05:25 GMTJobe Giles

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I really tried to get clearer images. It’s very tough because the green crystal is almost nearly invisible to the naked eye. This is an image of it with my iPhone on full zoom looking through a 30x loupe. So probably close to 40-50x magnification. 

28th Feb 2020 15:22 GMTJobe Giles

I think this one may be Aeschynite-(Y), fits with the other conclusions as a common associate.

28th Feb 2020 19:38 GMTFrank K. Mazdab Manager

I've never seen any members of the aeschynite/euxenite/polycrase/samarskite families (or related families) that weren't black (unless coated by brown alteration), pitchy-lustered, and most importantly, opaque.

28th Feb 2020 21:47 GMTJobe Giles

There are images of better looking version here. Also, note that this would have been encased in a quartz crystal up until extraction when the crystal was broken exposing the inclusion.

28th Feb 2020 21:54 GMTHarjo Neutkens Manager

Some of the aeschynite xx from Alpine-type clefts in the Hopffeldboden in Austria are transparent and have a similar light brown, yellowish colour. The habit is very similar too.
They typically occur in clefts that also contain titanite and monazite, among others.

28th Feb 2020 22:54 GMTJobe Giles

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Harjo, that is fascinating. What pointed me in this direction was a document I was reading about pegmatite classification. In looking at the pegmatite type delimitations, I was looking based on the proposed ID’s of the minerals above and found the only one that included rutile and tourmaline. 

28th Feb 2020 23:11 GMTJobe Giles

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Here is a reticulated rutile cluster I found recently in another plate. We also find red rutile included in the quartz.

28th Feb 2020 23:15 GMTJobe Giles

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On the side of this plate that was float from an eroded pocket, thus the damage. 

29th Feb 2020 04:34 GMTJobe Giles

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What I presume is zircon. From the same pegmatite. 

29th Feb 2020 04:36 GMTJobe Giles

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The other side. 

11th Mar 2020 02:55 GMTJobe Giles

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Reticulated Rutile in Muscovite in front of a Monazite crystal on smoky quartz crystal.
 
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