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Geology/Dig Up a Rock Can you Please Tell Me what it is


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Unknown Rock
Unknown Rock  
I was Digging and found a silver Rock its very light weight and Hard like one. Can you tell me a little more about this? Thank you Felicia

I may be able to answer the question but I need you to do a few things.  I need to know where exactly you found the "rock".  I got my MS Degree in Geology from the CSM and worked in Colorado for many years so I am familiar with most of the mining districts. This "rock" looks like a refined piece of metal not a naturally occurring "rock". Other things that I will need:   

1) Hardness of the rock.  Hardness of a rock is based on what mineral/rock type will scratch another mineral/rock type.  Since you don't have ten different minerals, that make up that scale, you can use some artificial harnesses from common things.  The scale goes from 1 to 10 with talc = 1 and diamond = 10, but you can use common things to determine hardness.  Your fingernail =~ 2; penny =~ 3; knife blade = 5.5.  Scratch your rock and tell me what its hardness is.  It will probably be > 5.5,  but let me know if a knife blade scratches it.

3) I need to know the streak of the rock.  The streak is the color of the rock when the rock is scratched by porcelain.  If you can find a piece of porcelain and scratch the rock on the porcelain the color that shows up on the porcelain is the streak.  If you have or can find a piece of porcelain, fine, but if you can't you might want to get what is called a streak plate; they are in-expensive and particularly if you like rocks in-valuable in determining rock types.  If the rock has iron in it it the streak will be red, brown or brownish red.

4) The last thing that I need to know and you may or may not be able to do this - is the specific gravity; you said that the specimen is light - how light.  The specific gravity of a rock is its weight relative to volume.  The standard is water which has a specific gravity of one.  The way that you determine the specific gravity, without a jolly balance (a machine used for this purpose), is somewhat complicated.  You need to find a beaker (graduated in metric) large enough to contain the rock.  Fill the beaker with enough water to cover the rock.  Take a measurement of the water level.  Add the rock and take another measurement of the water level.  Subtract one from the other; which gives you the quantity of water displaced.  Determine the weight (or mass) of the rock.  Divide the weight by the water displaced.  This will give you the rough Specific Gravity.

Let me know you answers.


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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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