What kind of rock is this?

[NathanD]

At its longest point, it's about the size of a baseball's diameter. Found it sitting on a railing while I was taking a walk on a river trail near me and thought it looked really interesting

Edited January 9, 2019 by NathanD

[LaurieAG]

Probably some form of Obsidian.

https://en.wikipedia.org/wiki/Obsidian

[DrP]

3 hours ago, LaurieAG said:

Probably some form of Obsidian.

https://en.wikipedia.org/wiki/Obsidian

Or a large tektite? 

https://en.wikipedia.org/wiki/Tektite

3 hours ago, NathanD said:

Found it sitting on a railing while I was taking a walk on a river trail near me and thought it looked really interesting

My guess would be that it was placed there by human hands who also thought it was an interesting rock.  

 

[HB of CJ]

Some sort of Obsidian/Shiest conglomerate?  How would THAT be possible?  Interesting "bubble craters".  Or are they impact artifacts? 

[John Cuthber]

Based on very lille but the colour and lustre, I'd wonder about furnace slag.

https://dlynx.rhodes.edu/jspui/handle/10267/2234

[LaurieAG]

23 hours ago, DrP said:

Or a large tektite? 

https://en.wikipedia.org/wiki/Tektite

There is one way to find out DrP, from the tektite link.

Quote

The difference in water content can be used to distinguish tektites from terrestrial volcanic glasses. When heated to their melting point, terrestrial volcanic glasses turn into a foamy glass because of their content of water and other volatiles. Unlike terrestrial volcanic glass, a tektite produces only a few bubbles at most when heated to its melting point, because of its much lower water and other volatiles content.

 

[DrP]

5 minutes ago, LaurieAG said:

There is one way to find out DrP, from the tektite link

Yea -thanks.  From the same link it also mentions about phenocryst content which can be assessed visually apparently... They are still obsidians though like you suggested in the first reply.  I can't tell from the photo if the lighter areas on the black rock are just chips and marks or actual phenocrysts.

 

On ‎1‎/‎9‎/‎2019 at 5:54 AM, NathanD said:

Found it sitting on a railing while I was taking a walk on a river trail near me

Are there similar rocks in the area? I guess you could also get a geological map of the area to see what sort of rocks you would expect to find to see if it fits with anything know to be common there.