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Geology/Found black stone deep in the ground


Black rock
Black rock  

Black rock back
Black rock back  
I fount this stone as I was planting trees in my yard. I live on Long Island New York.  I tried to melt it to make sure it was not plastic and it did not burn but it set off little tiny  crackle sparks.
Ill send picture.  What is it? Is it worth anything?

Long Island, as part of the Outer Lands region, is formed largely of two spines of glacial moraine, with a large, sandy outwash plain beyond. These moraines consist of gravel and loose rock left behind during the two most recent pulses of Wisconsin glaciation during the Ice Ages some 21,000 years ago (19,000 BC). The northern moraine, which directly abuts the North Shore of Long Island at points, is known as the Harbor Hill moraine. The more southerly moraine, known as the Ronkonkoma moraine, forms the "backbone" of Long Island; it runs primarily through the very center of Long Island, roughly coinciding with the length of the Long Island Expressway.

The land to the south of this moraine to the South Shore is the outwash plain of the last glacier. One part of the outwash plain was known as the Hempstead Plains, and this land contained one of the few natural prairies to exist east of the Appalachian Mountains.

The glaciers melted and receded to the north, resulting in the difference between the North Shore beaches and the South Shore beaches. The North Shore beaches are rocky from the remaining glacial debris, while the South Shore's are crisp, clear, outwash sand. Jayne's Hill, at 401 feet (122 m), within Suffolk County near its border with Nassau County, is the highest hill along either moraine; another well-known summit is Bald Hill in Brookhaven Town, not far from its geographical center at Middle Island. The glaciers also formed Ronkonkoma Lake in Suffolk County and Lake Success in Nassau County, each a deep kettle lake.

I tell you this to inform you that, since Long Island is a moraine outwash, the rocks there can consist of every type that is now contained on the Canadian Shield.  With this said the rock looks like obsidian.  

Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock.  It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth. Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) induces a high viscosity and polymerization degree of the lava. The inhibition of atomic diffusion through this highly viscous and polymerized lava explains the lack of crystal growth. Obsidian is hard and brittle; it therefore fractures with very sharp edges, which had been used in the past in cutting and piercing tools, and has been used experimentally as surgical scalpel blades.

Below is a site of obsidian images. You might want to compare these images to your rock.

The back of the rock is probably coated with another mineral.  If you kinda chip the surface you will probably find that the rock is shinny just like the other side.


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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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