Jdeutsch Posted January 7, 2018 Share Posted January 7, 2018 I was in an agate field in South Dakota just south of Badlands Park. Cretaceous era. I collected a few not-so-special agates and some jasper, and the pictured rock, which I thought was wind polished jasper- but it broke and had what looks to be brachiopods inside. I assume this is sedimentary or metamorphic. What is the relation between the agates in this region and the kind of specimen here? Why are there so many agate fields in this area of S Dak? Link to comment Share on other sites More sharing options...
ynot Posted January 7, 2018 Share Posted January 7, 2018 The rock with the brachiopods is most likely a quartzite sandstone. Similar in appearance but formed through different conditions. Agate and jasper are very common throughout the western United States. Most likely because of all the volcanic activity which caused much hydrothermal activity that led to the deposition of the agates and jaspers. 2 Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
abyssunder Posted January 7, 2018 Share Posted January 7, 2018 It looks more like chert to me, rather than agate. " We are not separate and independent entities, but like links in a chain, and we could not by any means be what we are without those who went before us and showed us the way. " Thomas Mann My Library Link to comment Share on other sites More sharing options...
ynot Posted January 7, 2018 Share Posted January 7, 2018 1 minute ago, abyssunder said: It looks more like chert to me, rather than agate. Wrong fracture pattern for agate or chert. Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
abyssunder Posted January 7, 2018 Share Posted January 7, 2018 I just read this : " The agates are encased in chert nodules housed within the lower Minnelusa Formation (Paleozoic: Pennsylvanian). I suppose these nodules are the result of silica-rich meteoric waters circulating through the unit with resulting diagenesis producing the chert. Why some nodules are agatized—I don’t have the slightest idea. Just as I am uncertain how/why agates really form! The formation of agates in several types of rocks is extremely complicated, even for the “experts”. " 1 " We are not separate and independent entities, but like links in a chain, and we could not by any means be what we are without those who went before us and showed us the way. " Thomas Mann My Library Link to comment Share on other sites More sharing options...
ynot Posted January 7, 2018 Share Posted January 7, 2018 3 minutes ago, abyssunder said: The agates are encased in chert nodules Never heard of this type of association before. Would like to hear more about it, because what I know of agates does not fit well with cherts. Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
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