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Identity HelpIlmenite/rutile

25th Feb 2012 23:40 UTCDon Saathoff Expert

Earlier in the week I posted a question in the "Education" forum asking about the probability that the pale-yellow to white accicular xls appearing to be epitaxial on anhedral grains of ilmenite could be rutile. I've attached two pics, different magnifications of the same cluster, (center of pic), for visual ID. Longest needle is ~1.5mm in length, black "blebs" are ilmenite and the blue mass below the cluster is hematite (specular & blue by reflection of window-light). Location is Beryllium Virgin claim, Paramount Canyon, Sierra Co., NM

Any help would be appreciated....optically, rutile is a strong possibility...

26th Feb 2012 16:10 UTCsteven garza

Dear Don;

VERY interesting, but, I doubt rutile as an ID; more likely araogonite or even calcite. Have you tried testing a single needle? I clicked to enlarge the pic, didn't see enough to judge, so, I changed "view" to zoom in at 200X, which did the trick. Those definitely look more like aragonites, than anything else. I don't see a tetragonal outline to the xls; I do see an orthorhombic outline, though. I know it's not on the mineral list for the locale, but, that's what I think it is. A new list inclusion would be cool, wouldn't it?

Your friend, Steve

26th Feb 2012 16:53 UTCRonald John Gyllenhammer Expert

Hi Don,

Thanks for the images. I agree with Steve that this is probably not rutile and more likely Calcite after Aragonite. I think it would be prudent to look for fluorescence under a UV lamp and also to put some grains to the test for a carbonate.

Ron

26th Feb 2012 18:22 UTCDon Saathoff Expert

Hello Steve & Ron,

Under crossed polars in the petrographic 'scope the birefringence didn't seem nearly high enough for either calcite or aragonite - in the .017 range and, because of the prefered orientation of the grains (and my student-grade 'scope) I could not get a good optical figure to determine either sign or character and, in reality, since I can't be sure of the thickness of the grains, the birefringence may be higher. My range of immersion oils is limited so RI determination is limited but with oil RI=1.775 the relief seemed to be moderately negative so you are both probably right and I'll sacrifice another xl for a carbonate test. Considering the environment and past lack of any carbonates I didn't even consider the possibility!!

Thanks! and I'll post the results of the carbonate test later...

Don

27th Feb 2012 19:39 UTCDon Saathoff Expert

OK folks, not a carbonate!! And I have a confession....the Taylor Creek rhyolites all look very similar and Cookie & I, with a friend, collected at the Beryllium Virgin, the Squaw Creek Tin Mine and the "Clearing", all on the same trip. All locations in the Taylor Creek rhyolite and all with similar mineralogies BUT only ONE has reported micro accicular TOPAZ. Somehow a couple of samples from the Clearing got mixed in with the Beryllium Virgin material. I emailed the pics to our friend and her comment was that "those xls look exactly like the topaz fro the Clearing".

And the optical matches.....so much for colorless rutile!!!

Don

27th Feb 2012 20:41 UTCRonald John Gyllenhammer Expert

Hi Don,

Good to hear that you have resolution on this! I've read about the very small radiating acicular topaz at "The Clearing" but I have never actually seen them. Thanks for the fine post.

Ron

27th Feb 2012 21:38 UTCJohn Sobolewski Expert

Don, these nedles look identical to mordenite that I have collected at Squaw Creek, Mordenite is pretty common in some ares there. John S.

27th Feb 2012 21:42 UTCCraig Mercer

Wow !! accicular topaz, that's intense Don.

Good to see resolve after guesses, can now be enjoyed.

28th Feb 2012 00:30 UTCDon Saathoff Expert

John, thanks! RI for mordenite is too low and birefringence is WAY too low compared to these xls....

Don

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