herb
spending too much on rocks
Member since November 2011
Posts: 444
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Post by herb on Sept 25, 2021 14:34:47 GMT -5
I came across these guys while searching thru some buckets in the basement and was wondering if anyone can tell me what they are. They are rather heavy for their size. The Specific Gravity is about 3.12. The color is a dark brown with blackish areas. The texture is a little rough. Based on their weight and color, I thought there might be some iron in them but a magnet is not attracted to them. They almost look like fossils to me, but I suspect the patterning is actually from water action. I found 1 piece that was broken and it shows a most interesting outer rind with a plain interior. The rind looks like whatever it is made of is radiating out from the center. Pictures show them dry and wet. The upper one is about 3.5 inches wide and the lower one is about 2.25 inches IMG_5821 by Shiny Objects, on Flickr IMG_5824 by Shiny Objects, on Flickr This one is about 5.5 inches wide IMG_5814 by Shiny Objects, on Flickr IMG_5816 by Shiny Objects, on Flickr The interior. About 1.75 inches wide IMG_5818 by Shiny Objects, on Flickr IMG_5820 by Shiny Objects, on Flickr Wet only. about 3.75 inches wide IMG_5811 by Shiny Objects, on Flickr
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rewdownunder
spending too much on rocks
Member since March 2012
Posts: 357
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Post by rewdownunder on Sept 25, 2021 14:50:13 GMT -5
Those look like ironstone concretions from out of a sandstone. Just because something has iron minerals in it does not necessary make it magnetic. Great photos, the cross section really helps with the ID. It should be harder than glass and leave a red streak. Very common in the geologic record but will not take a polish.
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Post by fernwood on Sept 25, 2021 15:13:38 GMT -5
Photos are great and I agree with above ID.
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Post by rmf on Sept 30, 2021 10:45:50 GMT -5
herb to chime in with rewdownunder the outer "skin" looks like Septarian where the mud has shrink cracks, but the Iron content is evident. Many of the ironstone concretions are composed of siderite which is a Iron carbonate. these are typical in Cretaceous sediments in TN, MS, TX. Also in the Pennsylvanian sediments like Mazon Creek in IL and Knob Knoster in MO. These kind of concretions have a lot of sand, silt, mud mixed in with the siderite so not typically magnetic.
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herb
spending too much on rocks
Member since November 2011
Posts: 444
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Post by herb on Oct 1, 2021 9:32:53 GMT -5
Thanks for the additional information! I always assumed that anything with a decent amount of iron in it would attract a magnet. But apparently that is not the case. Good to learn something new! herb to chime in with rewdownunder the outer "skin" looks like Septarian where the mud has shrink cracks, but the Iron content is evident. Many of the ironstone concretions are composed of siderite which is a Iron carbonate. these are typical in Cretaceous sediments in TN, MS, TX. Also in the Pennsylvanian sediments like Mazon Creek in IL and Knob Knoster in MO. These kind of concretions have a lot of sand, silt, mud mixed in with the siderite so not typically magnetic.
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victor1941
fully equipped rock polisher
Member since November 2011
Posts: 1,975
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Post by victor1941 on Oct 2, 2021 20:47:01 GMT -5
If you want a gloss try an acrylic spray. It might take two coats but these have a very interesting pattern and would make a nice display.
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