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Help identifying this....
  
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Bigkingman




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PostPosted: Jun 15, 2017 21:50    Post subject: Help identifying this....  

I have looked all over the internet trying to identify this rock I found while I was fishing today. I'm from Northern part of the flint hills in Kansas, I was fishing a long a river at the base of 30ft "cliff" made of layers of sedimentary rock. As you can see from the attached pictures I found it in a layer of soft almost mud like sediment in the cliff. The rocks hardness is around a 5 ( I scratched it with a knife) and feels to weight about the same as piece of limestone around the same size. Thank you for the help.


IMG_0137.JPG
 Mineral: ?
 Dimensions: Various
 Description:
 Viewed:  2177 Time(s)

IMG_0137.JPG



IMG_0139.JPG
 Mineral: ?
 Dimensions: Various
 Description:
Where I found it in the cliff
 Viewed:  2170 Time(s)

IMG_0139.JPG


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Bigkingman




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PostPosted: Jun 15, 2017 21:53    Post subject: Re: Help identifying this....  

Another picture


IMG_0138.JPG
 Description:
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IMG_0138.JPG


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Bob Harman




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PostPosted: Jun 15, 2017 22:11    Post subject: Re: Help identifying this....  

Given the sedimentary origins and appearance of the example, it appears as a calcite nodule with some iron staining. BOB
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Riccardo Modanesi




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PostPosted: Jun 16, 2017 01:09    Post subject: Re: Help identifying this....  

Hi Bob!
Have you tried with vinegar or chloridric acid? Does it fizz?
Greetings from Italy by Riccardo.

_________________
Hi! I'm a collector of minerals since 1973 and a gemmologist. On Summer I always visit mines and quarries all over Europe looking for minerals! Ok, there is time to tell you much much more! Greetings from Italy by Riccardo.
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Bigkingman




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PostPosted: Jun 20, 2017 07:59    Post subject: Re: Help identifying this....  

It does not fizz at all
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Dale Hallmark




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PostPosted: Jun 20, 2017 08:09    Post subject: Re: Help identifying this....  

Might it be Siderite? Just a stab in the dark.

Dale
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Pete Richards
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PostPosted: Jun 20, 2017 09:00    Post subject: Re: Help identifying this....  

Three likely minerals come to mind, all of which don't exactly fit what you have reported.

1. It's gypsum. With a hardness of 2 on the Mohs scale, it is softer than many other minerals that can be scratched with a knife. Break up one of the "biscuits". See if a sharp corner will scratch a penny. If you can find a nice flat surface (and gypsum should break in a way that forms these flat surfaces [cleavage]), you should be able to scratch it with your fingernail. Thin slabs can be bent somewhat without breaking and will stay bent.

2. It's calcite. Hardness of 3, so still can be scratched by a knife (hardness about 6). Also breaks giving smooth surfaces in several directions, yielding blocks that look a bit like distorted boxes. Finger nail will not scratch it, it will scratch a penny with difficulty. Should fizz in acid, and you tried this but perhaps your acid was too weak to produce much fizzing. Try it with some powdered sample and slightly warmed vinegar or lemon juice.

3, It's barite, though it does not look like it to me. Barite is substantially heavier than "normal rocks" but this can be hard to judge if you have minimal experience. It's about the same hardness as calcite, and also has cleavages in several directions, tending to form platy chunks. Will not fizz in acids.

Try your tests again. Look up the Moh's scale of hardness, and try hardness tests with some additional test materials. With this information, you should be able to figure it out!

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Collecting and studying crystals with interesting habits, twinning, and epitaxy
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Bob Harman




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PostPosted: Jun 20, 2017 11:49    Post subject: Re: Help identifying this....  

Like PETE R I still think the nodule could still be iron stained calcite or gypsum or even its relative anhydrite that has become iron stained. I just do not see that nodule either being siderite or barite.
I also suggest repeating the acid test with stronger muriatic acid dripped directly onto the nodule. If + then it will be calcite. If -- then I think gypsum is a good bet, especially if soft to a fingernail scratching it.
The picture context of the nodules being in bedded sedimentary matrix in the US Midwest is important here. BOB
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Riccardo Modanesi




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PostPosted: Jun 21, 2017 10:17    Post subject: Re: Help identifying this....  

Hi to everybody!
Siderite DOES fizz with acid, and baryte feels heavy in your hands! Gypsum is too soft according to what Bigkingman says. I think further tests are necessary.
Greetings from Italy by Riccardo.

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Hi! I'm a collector of minerals since 1973 and a gemmologist. On Summer I always visit mines and quarries all over Europe looking for minerals! Ok, there is time to tell you much much more! Greetings from Italy by Riccardo.
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Dale Hallmark




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PostPosted: Jun 21, 2017 10:46    Post subject: Re: Help identifying this....  

It was always my understanding that Siderite will fizz in heated 10% HCl. I assumed that to mean it would be very weak fizz in cold HCL if at all noticeable and likely not at all in milder acids. Anyway it was just a guess, I have no experience directly with Siderite.

I think it is interesting looking whatever it turns out to be.

Dale
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Bigkingman




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PostPosted: Jun 21, 2017 13:35    Post subject: Re: Help identifying this....  

It does not fizz, I've tested it with vinegar, lemon juice and another acid from a chemistry lab. However after using my finger nail and scratching it really hard with it it does scratch. Gypsum is very prevalent in this area of Kansas, there is long history of mining it here. I did find next to where I found these rocks water seeping from the layer. I don't know if that gives any clue of what it might be. Thank you all for the suggestions.
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