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Geology/What is this rock?



I am a forester in Southwestern PA, and found this rock sitting on top of the ground in a forest miles from the nearest house or road.  It has a hollow sound when tapped on, and the broken pieces show a grayish shiny inside that feels "glassy."  Any idea what it is?

This rock/bolder appears to be a piece of highly weather limestone; see the below picture links of weathered limestone(for whatever reason I could not copy and paste).

You might also look at the below site which shows the geology of Southwestern PA.  There are limestones within several of the formations in Southwestern PA; particularly the Pittsburgh Formation.  If you are in the area again you might take a eyedropper of HCl (Hydrochloric Acid) or Muric Acid (which is 10 percent hydrocloric that you can get at Home Depot or Lowes used to clean the lime off of masonry walls).  If you put acid on this rock and it is limestone it will efferess or bubbles it is limestone.

If the rock is broken through out it will sound hollow when tapped.  


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Joe Norris


I am an economic geologist. An economic geologist does mineral evaluations and appraisals of mineral or mining properties. I can tell you if your deposit has value - remember that a mineral deposit, no matter how good, only has value when mined. Any value assigned to a mineral deposit, in the ground, is only the speculative value that deposit.


I have been a economic geologist for most of my 35 year career. Although I have done work in perhaps 45 states and numerious countries much of my work has been in Appalachian coal, intermountain west gold and silver, and Arizona uranium.

Past President of the Virginia Section of the American Institute of Professional Geologists and a certified geologist in twelve states.

BS Degree from Eastern Kentucky University. Work on MS Degree @ Eastern Kentucky University, Colorad School of Mines & Marshall University Numerious short courses on the value of mineral deposits and how to value same. Also several short courses dealing with the different types of geologic processes; sedimentary, igneous, metamorphic along with the mineral associated with each.

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