Flint(?) Concretion

Terri

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#1
This concretion is about 3cm. in diameter, it really looks like flint to me, I'm sure I could be wrong and I think I may be be seeing conchoidial fractures. The concretion formed around a nucleus that appears to have some structure, wether it's a fossil or not I don't know. :roll: I really expected the outside of concretion to sizzle, but it didn't, neither did the black flinty looking stuff nor did the nucleus. Any insight appreciated! :smile:
 

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DWhatley

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#2
Is that as round as it looks in the picture? I have seen lots of rounded rock but not rocks that are round so it really stands out. Could be something man shaped as a weapon?
 

Terri

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#3
Yes, it's my understanding that concretions can be perfectly round. I've had this for years and just enjoyed it but my curiousity got the better of me and I decided to crack it. I wasn't expecting to see the flintlike material or such a cool nucleus (possibly fossil?). Hopefully Kevin will clear things up. 8-)
 

Terri

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#5
:oops: I went round and round (pun intended) :heee: on wether to call this a concretion or a nodule. What I read was that concretions always form around a nucleus, and when I searched nodules they were mostly oddly shaped formations. So I'm incorrect? :confused:
 

DWhatley

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#6
Kevin,
Can you explain the difference in what you would see between a geode and a nodule. I read the Wickipedia distinction but it was not clear how you would visually determine if the core was coated or formed as part of the rock (correct this undersanding of the differences if my paraphrase does not properly match the concept :oops:). Include in your tutoring how you would determine that this is not a geode please :sagrin:
 

Terri

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#7
I'm finding what seems to be a lot of contradictory information on nodule vs, concretion. I thought I had it penned down to concretion, but I will gladly concede to Kevins superior knowledge. :razz:
 

Architeuthoceras

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#8
DWhatley;187930 said:
Kevin,
Can you explain the difference in what you would see between a geode and a nodule :sagrin:
A geode is hollow with crystals growing inside. A geode is a nodule that is hollow. :heee:

Terri;187931 said:
I'm finding what seems to be a lot of contradictory information on nodule vs, concretion. I thought I had it penned down to concretion, but I will gladly concede to ... :razz:

The best explanation is found HERE
Also see Siderite and Phosphate concretions/nodules.

To me, generally, concretions are large and soft(er) and nodules are small and hard. :sly:
 

Terri

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#11
Well, after reading the great link you supplied, of course you would be correct, chemically speaking. Technically, I should have called it chert. I read this article and based the decision to call the material flint on color and texture instead of chemical makeup. http://www.quartzpage.de/flint.html

So, the differences in cryptocrystalline quartz, chalcedony, chert and flint would be crystal size and specific gravity and are nearly identical in chemical makeup to that of pure quartz. 8-)

Thanks again Kevin!
 

DWhatley

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#12
:sagrin: so does that make it a geode if the cryptocrystalline quartz, chalcedony, chert, flint had larger crystals and a hole in the center? :roll:
 

Terri

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#13
I believe, basically, you would be right. But I bet we could make it a whole lot more complicated than that if we wanted to.:heee:
 

DWhatley

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#14
At least it is just a little more sophisticated than calling it a round thingy :biggrin2:
 

Solius

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#18
Terri;187974 said:
So, the differences in cryptocrystalline quartz, chalcedony, chert and flint
Hi all. First post.

I was taught that chert, flint, jasper, ect are colloquial terms for the mineral chalcedony which is composed of micro-crystalline SiO₂. Too, geodes have chalcedony rinds or they are just nodules. I have seen geodes with several generations of xl formation that led to total filling of the cavity.

Things might have changed. It has been 25 years since mineralogy and I haven't really kept up.
 

DWhatley

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#20
... and I am just trying to translate the concepts into something simple enough to follow and relate :oops:
 

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