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A general guide for using the Forum with some rules and tips
Please identify - rock with white inclusions
  
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foreman




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PostPosted: May 01, 2018 23:04    Post subject: Please identify - rock with white inclusions  

The railroad in my local town(near Harrisburg, PA) has a town of dark gray rocks. A minority have white stone inclusions. The hardness is not as strong as the gray stone, but not soft either.

Doesn't appear to be like anything I've seen before. Any thoughts on what this might be?

Thanks



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foreman




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PostPosted: May 01, 2018 23:22    Post subject: Re: Please identify - rock with white inclusions  

The gray appears to be limestone. Looking to ID the white
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Jordi Fabre
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PostPosted: May 02, 2018 04:25    Post subject: Re: Please identify - rock with white inclusions  

As you are a new user you can't be faulted for not being familiar with the "rules" which are probably more like guidelines. When submitting something like photos, it is standard practice to always provide as much information as possible, thereby greatly improving the prospects of getting meaningful responses. You are welcome to post identification requests about mineral specimens on FMF, but if you want us to help you there are a few tests you should do and information you should provide. It will help us a lot and you'll learn a lot as well:

1 - Read the Asking: "What is this? / Where is it from?" topic. It contains information about basic tests. These tests are very important in identifying a mineral. Without them, our guesses might be meaningless as different minerals look the same in photos. The motto is: the more accurate the information, the better the answer. And please do not neglect to state the locality where the specimen was found, this is a great help in suggesting an identification.

2 - Then, read A general guide for using the Forum with some rules and tips It contains posting tips and a few basic rules about FMF we invite you to follow. Regular members do this. In your doing it too, you'll quickly be considered as a member of our friendly community.

In case you need even more help you can use this fine web page from Minsocam.org, the Mineralogical Society of America.

Cheers

FMF Administrators' Team
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Bob Harman




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PostPosted: May 02, 2018 06:16    Post subject: Re: Please identify - rock with white inclusions  

Your poor quality photo appears to show a fine grained, relatively resistant limestone railroad ballast. Googling this shows a number of similar examples. Here in Indiana we have similar material. Jordi's ideas for testing are appropriate, but have limitations. Your example, while a non-crystalline limestone, is considered a rock as it has impurities and inclusions that most interest you. Putting the ballast in vinegar will show vigorous fizzing as it is a carbonate, but the inclusions, that you are interested in, will be lost as part of the overall vigorous fizzing.

Based just on your photo here are my thoughts. The basic ballast is limestone. The whitish inclusions most probably are silicified (quartz replaced) tiny bits of invertebrate fossil remains including crinoid stems, shells and other brachiopods etc. These bits are so small as to be largely unrecognizable. Most of these ballast limestones also include tiny flecks of shiny golden pyrite; if you examine a bucket load of pieces you might find a tiny fleck or two.

The other possibility is an evaporite mineral such as epsomite. When the host rock is totally and completely dry, the epsomite crystalizes as a whitish thin film on the surface. If the rock is wetted, the evaporite mineral immediately dissolves, only to reappear when the rock again totally dries out.

Only fresh ballast is the good example for testing and examination, as long standing ballast will get contaminated and darker due to being stained with oil and lubricant drippings from the many passing trains.

Hope this helps. BOB
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foreman




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PostPosted: May 05, 2018 17:48    Post subject: Re: Please identify - rock with white inclusions  

Yes, I did scan the guidelines. I provided what information I could including my location, but as this rock was found in an area placed by man, and not natural from a dig, it's not too helpful.

Thanks for the info Bob. I did forget to mention this one was found by the Susquehanna river which runs parallel to the rail tracks.

I considered this may be white limestone, however the texture is completely different as is the hardness. The theory that this may be silicified fossil material is interesting. I broke some up and it crumbles into interesting shapes much unlike other minerals I've crushed..

I have yet to see pyrite or any other interesting inclusions in any of the limestone ballast.

I can mail a small sample if anyone is interested and can help identify. I can try to get a better picture of the crushed white material.
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foreman




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PostPosted: May 23, 2018 00:54    Post subject: Re: Please identify - rock with white inclusions  

Found another specimen


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foreman




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PostPosted: May 25, 2018 20:21    Post subject: Re: Please identify - rock with white inclusions  

A local mineral club member thinks the white is calcite.
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crosstimber
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PostPosted: May 26, 2018 10:08    Post subject: Re: Please identify - rock with white inclusions  

Hello Foreman,

A drop of vinegar or dilute hydrochloric acid will confirm whether this is calcite or something else. When exposed to the acid, calcite will react producing bubbles. A hardness test will also help. Calcite is relatively soft and can be easily scratched with a knife blade.

Michael
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