rockstock
spending too much on rocks
Member since April 2019
Posts: 472
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Post by rockstock on Oct 28, 2019 11:40:35 GMT -5
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Deleted
Deleted Member
Member since January 1970
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Post by Deleted on Oct 28, 2019 13:22:51 GMT -5
Possibly schorl tourmaline, if they are multiple xtls bundled together. However, I'm thinking something else, as they don't seem to have any faces that resemble tourmaline. I know that tourmaline can occur in metamorphic rock (including marble), but not sure of conditions that would be conducive for it forming in limestone. What looks like the ends of the rods also aren't clean as I'd expect for most mineral xtls, even when broken. Perhaps carboniferous fern stems or something else organic (for instance, I've seen fossil horsetail reeds in my area that looked somewhat similar to that). I'd want to go back to wherever found and see if I could find more associated pieces (or even crack it in half to get a look at potential unweathered surfaces).
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rockstock
spending too much on rocks
Member since April 2019
Posts: 472
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Post by rockstock on Oct 28, 2019 13:23:11 GMT -5
Soaked it in a little bit of acid, didn't change or reveal much, but did bubble a lot.
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gemfeller
Cave Dweller
Member since June 2011
Posts: 3,759
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Post by gemfeller on Oct 28, 2019 13:42:43 GMT -5
Tourmaline in limestone? I think not. I think R2D is right when he suggests a fossil of some sort.
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Post by RickB on Oct 28, 2019 16:09:36 GMT -5
Read this on the GIA (Gemologist Institute of America) website under tourmaline.
"Uvite is rich in calcium, magnesium, and aluminum. Dravite is rich in sodium, magnesium, and aluminum. Both form in limestone that’s been altered by heat and pressure, resulting in marble that contains accessory minerals like tourmaline."
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gemfeller
Cave Dweller
Member since June 2011
Posts: 3,759
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Post by gemfeller on Oct 28, 2019 16:38:09 GMT -5
RickB, yes, in metamorphosed limestone turned into marble. But plain limestone is sedimentary.
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Post by greig on Oct 29, 2019 12:23:15 GMT -5
Cool rock. I don't think it tourmaline from the pic. When you etched it, did it bubble in this area? I would think fossil if that is silica (no affect by the acid).
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rockstock
spending too much on rocks
Member since April 2019
Posts: 472
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Post by rockstock on Oct 29, 2019 12:43:44 GMT -5
Thanks for the info! Here's a pic with some acid added. Could be just a layer over what it is, that's bubbling. Figured it wasn't tourmaline but really looked like it, haven't seen a fossil like it yet, or til now!
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rockhoundoz
starting to spend too much on rocks
Member since March 2017
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Post by rockhoundoz on Oct 30, 2019 14:19:33 GMT -5
I find these in Kentucky & other midwest limestone as well, my best guess is aragonite pseudomorph, replaced by limestone or dolomite etc. Here's a picture of aragonite crystals that I found online from 'science photo library' not my picture: I should add that I also find brown aragonite crystals in the same limestone, though never yet with this column type shape though...
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thedude
off to a rocking start
Member since November 2019
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Post by thedude on Nov 26, 2019 11:09:56 GMT -5
Really depends where you found it(ie, location). It appears to me to be Cordites, a fossilized reed that was living during the Carboniferous period.
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