What The Heck Is This?

[midnightdsob]

[jasong]

Thought slag at first glance, but it appears to have some silicification occuring in the pore spaces. 2nd thought would be something volcanic, but zooming in I'm not sure about that either.

Looks more like something which had some mineral oxidize/erode out of it. Then water deposited that silicified/agate-y looking banded substance? Not sure what the rock itself is since it's so vuggy, porous, stained, and covered with secondary mineralization that it's hard to guess. 

Not sure if ore-type mineral, or something sedimentary. Could still be something volcanic too, with secondary mineralization. The geology of the area it was found in would probably lend clues.