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PhotosStrontianite - Minerva No. 1 Mine Ozark-Mahoning Group, Cave-in-Rock Sub-District, Illinois - Kentucky Fluorspar District, Hardin Co., Illinois, USA
4th Nov 2013 19:53 UTCRichard Gunter Expert
4th Nov 2013 20:44 UTCBob Harman
5th Nov 2013 03:23 UTCMark Heintzelman 🌟 Expert
MRH
STRONTIANITE Cave In Rock, Illinois ex B. Essleman Collection
STRONTIANITE, Strontian, Argyllshire, Scotland. Striated, crystallized mass from the Northwestern University Collection
It is a fair question, I also see "wheatsheath" calcite posted, a habit oft seen in Strontianite as well. Were it not one from Geoffrey Krasnov's collection I would wonder about the I.D. of that one as well.
5th Nov 2013 05:34 UTCHarold (Hal) Prior Expert
5th Nov 2013 13:49 UTCBob Harman
5th Nov 2013 15:16 UTCRichard Gunter Expert
5th Nov 2013 17:26 UTCEric Quinter
5th Nov 2013 17:58 UTCKelly Nash 🌟 Expert
5th Nov 2013 18:08 UTCRichard Gunter Expert
-------------------------------------------------------
> This looks more like the very steep rhombohedral
> Calcite than Strontianite. Are not all of the
> Strontianite crystals curved?
I can try SG but with the Fluorite and petroleum inclusions in the Strontianite/Calcite it may not be that clear-cut. It seems as if there are many examples similar to mine in the literature labeled as either Calcite or Strontianite.
5th Nov 2013 18:46 UTCDoug Daniels
5th Nov 2013 20:15 UTCTom Tucker
5th Nov 2013 21:12 UTCRichard Gunter Expert
These crystals are aggregates of approximately parallel prisms with irregular outlines down the c axis. The faces on the aggregates are so distorted that that type of crystallography is difficult.
5th Nov 2013 23:46 UTCAlfred L. Ostrander
I have three specimens of this material from the Minerva, acquired in 1973. It was rumored then that these were zoned calcite and strontianite crystals. If you have a LW blacklight, you can see the zoning. So, I was asking the same question a long time ago.
More to the point, analysis by J. Alexander Speer and Margaret L. Hensley-Dunn reported in the American Mineralogist (1976) indicated that strontianite from the Minerva #1 was 25 mole percent Ca. Traces of Pb and Ba were also indicated. The Ca is witin the accepted range for strontianite. So strontianite it is, at least for me.
Combine that chemical mess with the preferred habit of strontianite as long prisms terminated by a high order dipyramid with twinning common on the prism and you just don't see "normal" orthorhombic forms.
Curved strontianite is common but not necessary.
Best Regards,
Al O
5th Nov 2013 23:59 UTCRichard Gunter Expert
Thanks so much for the information. I will check the sample with LW UV and have a look at the American Mineralogist article. None of this data made it into the Mineralogical Record Special Issue on the Illinois Fluorite District.
6th Nov 2013 00:11 UTCRichard Gunter Expert
The aggregates have yellow zoned fluorescence in both SW and LW UV. I thought originally I was seeing the fluorescence of the petroleum inclusions but it looks like it is the Calcite-Strontianite aggregates are zoned.
7th Nov 2013 13:39 UTCAlfred L. Ostrander
I only mentioned LWUV because one specimen I has only responds to LW. You are correct about response to reaction to both in some specimens. I have no idea what percentage respond to LW only vs both LW and SW. And I'm still not sure if the response is entirely based on inclusions of petroleum.
Just an interesting side story here. I also acquired several very sharply formed fluorite clusters from the Minerva at the same time as the strontianites. The fluorite was rather dark and low in luster. I got them because of the very sharp form. When I got them home I looked at them under a microscope to see if anything was causing the low luster. It looked like there was a very thin film of something covering them. Water just beaded up on the surface. A quick drop of alcohol and wipe with a Q-tip proved it to be a very thin coating of hydrocarbons. Those things quickly (but messily) cleaned up very nicely revealing a very high luster. I had only purchased two small cabinet size pieces due to the low luster but the price was very low so why not? I quickly went back to the dealer and bought three much larger specimens at a very low price. They cleaned up just as the other specimens did. One of the larger pieces shows exceptional blue and yellow color zoning. Beautiful! None of these specimens showed any fluorescent response to the oily film on them.
I bring this story up because you never know what response you will get with UV of any wavelength. All I know for sure is that these Minerva strontianites sometimes show normal light color zoning, usually light brown and almost white patterns. Some that show little normal light zoning show clearer zoning under UV. I am assuming the strontianite rich zone is fluorescent. As Eric noted, a flame test indicates strontium but not how much. I tried separating out bits from each color zone and got positive flame tests from each for strontium.
I guess it all comes down to the fact that I like these spikey color zoned crystals and am comfortable calling them strontianite!
Best Regards,
Al O
7th Nov 2013 15:19 UTCRichard Gunter Expert
Sounds like a good idea. The zonation of colour and fluorescence seems to be the key to these. The Fluorite associated with my sample has a very high luster and is almost flawless. The colour varies with the light conditions but in sunlight is a light blue. It was probably cleaned before I bought it.
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