jamesp
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Post by jamesp on Feb 1, 2015 12:56:02 GMT -5
It, along with other variations were found in a drainage from a rich garnet district in the mountains of N Georgia. Are the pink spots garnet ? They are the color of the local Garnet. Are the black spots biotite mica ? Also common in this area. The black spots look dendritic more so than mica would. Felspar is not very common at this location, the granites are high in quartz content. And lots of gneiss with black in them. Quartzite is normally tectonically compressed sand I believe. In flat plates. This material has no waves in it. And the cobbles are straight or flat as if a worn plate. It is very dense and rings when tapped with a hammer, unlike the granites and gneiss'. Virtually fracture free. Cutting more variations, much of it blacker in background. Thanks in advance for comments. Another, frame is 1" X 2" And another, frame 1" X 2"
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Post by gingerkid on Feb 2, 2015 6:37:12 GMT -5
That's some of that Georgia Freckle Rock from them thar hills, jamesp. Could it be quartz monzonite? The same stuff at Stone Mountain (GA)? I think xXxAlisha91xXx lives near Elberton, but she hasn't posted in a long time. Sure do miss her!! Maybe she'll see your post and possibly have an answer for you. Carving of Stonewall Jackson, Robert E. Lee, and Jefferson Davis at Stone Mountain, GA "It is a quartz monzonite dome monadnock, the site of Stone Mountain Park in Stone Mountain, Georgia, United States, and the largest bas-relief carving in the world." Source: wikipedia
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Post by gingerkid on Feb 2, 2015 7:20:51 GMT -5
jamesp... en.wikipedia.org/wiki/Quartz_monzoniteMy apologies, James, I went out into left field instead of trying to answer your question. Although you mentioned that feldspar isn't usually found at the location, I wondered if the freckles/garnet-looking mineral is possibly a type of feldspar. ??
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jamesp
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Post by jamesp on Feb 2, 2015 9:52:42 GMT -5
jamesp... en.wikipedia.org/wiki/Quartz_monzoniteMy apologies, James, I went out into left field instead of trying to answer your question. Although you mentioned that feldspar isn't usually found at the location, I wondered if the freckles/garnet-looking mineral is possibly a type of feldspar. ?? excellent research Jan. I think this is a tough call. The felspar sure fits the bill. Felspar seeds ha. The color irritates me though. As does the way the quartzite under cuts around the 'seeds'. And the spacing. But it is normally the mineral found in our granitoids around here. Millions and billions of tons of it LOL. I was fighting the felspar, give me something new !! I will say that cracking a rock w/felspar usually shows cleavages at the felspar. I will look closer at the rocks I windowed for cleavage. But the spots are sort of like sprays or grain clouds instead of crystals. Which is strange for garnets or felspar. The 2nd photo is by far the most common type at this site. It sure looks like white quartz, biotite mica, and pink felspar. The common ingredients in our common pink granite. That comes in so many variations. I do see granite counter top material sprinkled with garnets. Used to romp those granite quarries around Stone Mountain. There is garnet and black tourmaline, and fairly common. But I think you got me convinced this is 'seeds of felspar'. I will go back and search further. The quartzite has potential there. thanks
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Post by gingerkid on Feb 2, 2015 11:24:34 GMT -5
jamesp, have you had a chance to look at your windowed pieces or have they blown away to Kansas with the wonderful cold wind we're having today? Just taking a guess at the feldspar. Definitely not qualified to make any calls.
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jamesp
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Post by jamesp on Feb 2, 2015 13:02:27 GMT -5
jamesp, have you had a chance to look at your windowed pieces or have they blown away to Kansas with the wonderful cold wind we're having today? Just taking a guess at the feldspar. Definitely not qualified to make any calls. Been outside since this morning, and it is cold. Hope the wind moves on to Kansas. I have sawed a few more. That is fancy granite. About sure of it. With high quartz percentage in the form of fused sand(quartzite). I would put it up against tight grained Tallahatta quartzite in mechanical properties, just a lot more decorative. I have found many quartzite spear heads and chip zones in TVA lakes. Some of it is spectacular. Those dang native guys would never tell me their source though. It is best found in the walls of creeks as a 1-5 inch flat layer. Tallahatta quartzite in Mississipi: miss-archaeology.blogspot.com/2007/08/tallahatta-quartzite-quarry-site-in.htmlGuessing from this drainage i found this material the source must be 30-40 miles upstream. It is well rounded and that is about the furthest distance of this drainage. It makes up maybe less than 1% of the cobbles in this river. And that would be the type in the middle photo. Knappers would love it, as it is perfect for that. Quartzite often breaks blocky, and the cobbles were blocky. I went to garnet riddled Rottenwood Creek located under intersection of I-75 and I-285 bridges and found this in a couple of hours. It has tons of quartzite plates. Could have done better if it was warm that day and could have gotten in the creek.: www.flickr.com/photos/67205364@N06/sets/72157639487638866
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Post by gingerkid on Feb 2, 2015 13:17:01 GMT -5
I'm glad that you found the answer to your question, jamesp! That's an interesting blog you linked to with the Tallahatta quartzite. Looks like they are having a good time looking for materials. Sure hope the wind dies down. Have you noticed the temps are steadily dropping?
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jamesp
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Post by jamesp on Feb 2, 2015 13:30:08 GMT -5
Yes temps are dropping. Humid and 20 mph. el yukko. come on spring I see the problem. My incandescent light is turning the pinky purple into felspar pink. ha These piece is blazing purple pink. I need to photo in sun. I'll take it what ever mineral it is though. Bad focus. See the layers, also typical of quartzite
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Post by gingerkid on Feb 2, 2015 13:37:44 GMT -5
That's a beauty. Hope you get a pic of it in the sunlight. I've realized that most of the pics I take of mineral specimens don't show accurate colors unless taken outdoors. Weird. Do you still think that the black mineral is biotite, jamesp?
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leadbelly713
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Post by leadbelly713 on Feb 2, 2015 14:40:35 GMT -5
The pink stuff could be orthoclase and the black stuff could be hornblende. Robert.
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Post by captbob on Feb 2, 2015 14:54:28 GMT -5
The pink stuff could be orthoclase and the black stuff could be hornblende. Robert. I was just gonna sign on to say hornblende as well. Had to check that it's common to Georgia first. It is.
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jamesp
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Post by jamesp on Feb 2, 2015 14:56:49 GMT -5
That's a beauty. Hope you get a pic of it in the sunlight. I've realized that most of the pics I take of mineral specimens don't show accurate colors unless taken outdoors. Weird. Do you still think that the black mineral is biotite, jamesp? leadbelly713 probably has it right. Hornblende. It is very common on this river. Never thought about hornblende. Lots of gneiss with hornblende in it. Looks like this, but much of it with needle crystals that reflect light off cleavage: Some of it mass hornblende with out any white quartz, black and glittery. Thank you leadbelly.
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jamesp
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Post by jamesp on Feb 2, 2015 14:59:48 GMT -5
Like this with garnets. I suppose pure hornblende. Some with 1/8 needles all compressed together.
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Post by captbob on Feb 3, 2015 10:27:04 GMT -5
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jamesp
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Post by jamesp on Feb 3, 2015 17:14:04 GMT -5
A beautiful combo, green and pink. Green matrix of zoisite makes it. Hornblende has specific gravity of 2.9-3.4, heavy stuff. It is real common in N. Georgia.
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jamesp
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Post by jamesp on Feb 3, 2015 17:36:50 GMT -5
A few more rare granitoid/quartzite materials from the same location. These are the densest rocks in the river, the rest are gneiss, hornblende and schist. Been around granitoids all my life. Higher elevation Appalachian rocks in this family can get quite bizarre. Garnet and felspar often recrystallize during metamorphic changes. These rocks may be such a situation called porphyroblasts. Garnetkid gingerkid ? pink felspar dots ? garnet dots ? Looking at porphyroblastic gneiss-anybody knowledgeable of such
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Post by fantastic5 on Feb 3, 2015 20:42:40 GMT -5
pink felspar dots ? The area you were collecting is known for zoisite. I showed this picture to my husband and he immediately offered thulite. I did a mindat search for thulite in that area and came up short. Possible??
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Post by gingerkid on Feb 3, 2015 22:45:13 GMT -5
The pink stuff could be orthoclase and the black stuff could be hornblende. Robert. Thanks, leadbelly713! jamesp, did you take any pics before you cut the garnet piece? I have a slab of uvarovite garnet in chromite. I don't know if that's garnets in your slab. From what I understand, garnet porphyroblasts are common. I thought of tsavorite when I read your post. Some of the tsavorite porphyroblasts look like baking potatoes with gorgeous green crystals to me. I don't know, but as fantastic5 suggested, maybe thulite? I found info about thulite found in Dekalb County. "The occurrence of thulite at Stone Mountain in DeKalb County, was reported informally by Dr. Alfred C. Hawkins. Dr. Frank A. Daniel of Atlanta, kindly supplied a specimen of pegmatite containing thulite from the Ethel quarry of the Ethel Granite Corporation, situated about two miles northeast of the carving on Stone Mountain. A thin section shows a few isolated grains of thulite, with very low birefringence, scattered irregularly through the plagioclase feldspar." @wampidy may be able to help confirm whether or not it may be thulite. Maybe garock and pghram may have some answers for all of us.
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Deleted
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Post by Deleted on Feb 3, 2015 23:04:29 GMT -5
I had never heard of thulite on the wrong side of the country but I have never researched it, just made stuff out of it. Somewhere between my second and fifth favorite rock. Jim
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jamesp
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Post by jamesp on Feb 4, 2015 5:53:31 GMT -5
Thanks you guys. I will saw more and post photos. Great food for thought, will research all mentioned on this end. Hard to beat more samples, so I will keep cutting and posting. gingerkid-Spent a lot of time around those quarries at Lithonia, Stone Mountain and Panola Mountain. There are small areas of variety, most is white granite. I hear reports of unusual occurrences, but it is a bit of a giant monoculture of white granite out that way. They remove so much rock, no telling what they have ground up for road gravel and rip raf.
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