Here's an interesting one for ya

[stdenis_jd]

So I found this guy in the middle of the lower peninsula, Michigan - it's obviously a syenite [plagioclase, feldspathoid (orange fluorescent sodalite), k-spar, biotite] familiarly called "yooperlite" but it displays minute amounts of orange fluorescence from the sodalite, but a widespread bright bluish-white fluorescence on LW UV (no reaction to SW).

I've posted this guy on a different site and didn't get the correct answer as to what this fluorescent mineral is. A great idea from a geologist was possibly natrolite polymorph after nepheline, but it didn't pass the HCL test (natrolite should partially degrade to a "gummy" substance). It also is not calcite which was my first thought since it did not react at all to HCL.

Hardness test is pretty much irrelevant since it appears to be a pretty thin film and will undoubtedly produce a false reading and of course SG is out of the question. Any other ideas? I'm thinking it must be original nepheline since these syenites are quite likely "nepheline syenites" anyway.

**EDIT** nevermind nepheline, I forgot it doesn't fluoresce

 

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[stdenis_jd]

oh yeah I forgot, nosean is another good possibility due to the bluish fluorescence

 

[fuss]

Are you referring to the teal colored splotches in the 3rd image or the brilliant blue that covers the rest of the rock?

 

[fuss]

Ill go ahead and assume you mean the splotches. Have you ruled out an organic?

 

[stdenis_jd]

Ill go ahead and assume you mean the splotches. Have you ruled out an organic?

yeah if it was organic it would either scrape off or react to or dissolve in acid. I put a pretty generous does of muriatic on it for a few minutes and nada.

As far as the fluorescence, the photography isn't great so the purple color is just a reflection of the UV light, not fluorescence. The fluorescent parts are white with a slight tinge of blue (colors didn't transfer well to the pic)

 

[fuss]

I have dozens of these rocks and a couple do show something somewhat similar to this. Since our UV lights are different it may be tough to compare, but if you go back to my post about the UV rocks I found in winter and look at the last image you can see some green/teal fluorescing, curious if it could be the same thing.

 

[stdenis_jd]

I'm thinking your green/teal could be a calcium coating, have you acid tested?

 

[fuss]

No reaction to HCL. Do you think that yours is only a surface feature or possibly runs throughout the interior?

 

[ToddsPoint]

You guys are way over my head, but keep talking, I'm learning. Gary

 

[Kray Gelder]

What Gary said.

 

[DDancer]

Might try an XRF reading of the points of interest and look for the defining materials in those sections. I'm proably mistaken but at LW only it reminds me of a phosphor. I cant hazard to guess but the picture comes off as teal in color not bright blue white. An artifact of the camera?

 

[stdenis_jd]

Might try an XRF reading of the points of interest and look for the defining materials in those sections. I'm proably mistaken but at LW only it reminds me of a phosphor. I cant hazard to guess but the picture comes off as teal in color not bright blue white. An artifact of the camera?

yep, exactly. One of these days I'll try to get on Fuss' level with the photography (which I need to do anyway) - personally his photos of fluorescence are the best I've seen.

As far as phosphates, I doubt it - I just don't see phosphates being a likely association. It was buried in sand in a gravel pit so I don't see it being introduced by man either. I'm reasonably certain it's some sort of feldspathoid, but what kind and is it a pseudo/polymorph?

Fuss - it is embedded in the rock itself, but it is superficial. I cut it into slabs and there is only a small amount of pinpoint orange fluorescence from the sodalite group. I suppose it's possibly a white variation of hauyne as well...it isn't always blue strangely enough.

I think without XRF or some other chemical analysis I'm dead in the water and stuck with speculation.

 

[fuss]

Thx man, appreciate the nice comment. Interesting that you cut them into slabs, do you plan on polishing them?

 

[smokeythecat]

XRD will be the only sure way. Those syenite bodies have stuff in them no one ever heard of before!

 

[stdenis_jd]

Fuss - yeah probably, eventually. The fluorescence isn't very good so I'm putting those on the back burner.

Smokey - you got that right! Syenite bodies yield some bizarre stuff. Charoite case in point. Syenitic magma intruded into limestone = chemically altered to purple & white feldspar, throw in some tinaksite and augite/aegerine for good measure. My favorite rock

 

[fuss]

Do you know what the orange/red mineral is found in these? I initially thought orthoclase but have my doubts.

Fuss - yeah probably, eventually. The fluorescence isn't very good so I'm putting those on the back burner.

Smokey - you got that right! Syenite bodies yield some bizarre stuff. Charoite case in point. Syenitic magma intruded into limestone = chemically altered to purple & white feldspar, throw in some tinaksite and augite/aegerine for good measure. My favorite rock

 

[A2coins]

You guys are way over my head, but keep talking, I'm learning. Gary

Mine too but its a cool view from way up here. lol

 

[stdenis_jd]

Do you know what the orange/red mineral is found in these? I initially thought orthoclase but have my doubts.

Yeah it's K-spar - with syenites like these with feldspathoids, quartz generally cannot exist (if you haven't researched/studied the QAPF diagram I strongly suggest getting familiar with it, it's a great tool) - the silicates get used up forming feldspars both ortho and plagioclase. Feldspars form first in the cooling of the magma.

Mine too but its a cool view from way up here. lol

 

[stdenis_jd]

I suppose "quartz deficient" is a better way to describe these kinds of syenites ^^