front face of rock

Hey all, I came across this rock in a river in Western New York. There are two different parts of this rock.

There are smooth, rounded parts that are brown to red in color. Their is a slight luster or sheen to these parts and are also magnetic. There seems to be very defined line where this rock meets the other - but the two types are well fused.

The other parts of the rock are very porous and covered in pits. Black in color, with small chunksof white here and there (no more than a few millimeters wise with the largest being maybe 5 to six millimeters. These parts range from matte to glass-like luster. Parts of the these regions of the rock are softer, while others in the more glass like sheen are significantly harder. I was able to completely remove a solid chunk of of the matte porous area and it left a clearly defined crater of significantly more sturdy rock. (Photo below)

It’d be great to hear some opinions on this. enter image description here


closed as off-topic by Jan Doggen, uhoh, Erik, Fred, Gimelist Aug 28 at 10:14

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  • $\begingroup$ Is the rock light or dense and does it crumble easily. Is it highly magnetic or weak? And do you know the exact location you found it at? Was it in the river or by its edge? $\endgroup$ – Armondo Villaescuza Sep 3 '18 at 17:58
  • $\begingroup$ It was in the river. The brownish parts do not crumble at all. The matte parts of the black part do, but the more glass like areas of the black do not. The brownish parts are fairly magnetic. Enough to feel a tug when placing a magnet to it. The magnet will stay in place without holding on to it - but it’s important to note that only the brown parts are magnetic. $\endgroup$ – Aisopoli Sep 3 '18 at 19:10
  • $\begingroup$ In addition, it doesn’t feel heavy for its size. It came out of Buffalo Creek in West Seneca, NY. Great place to find fossils - and whatever this is. I believe I may have found a second specimen of the same variety. $\endgroup$ – Aisopoli Sep 3 '18 at 19:27
  • $\begingroup$ how dense is it? It looks like a wad of burned plastic (also known as plastiglomerate, likely from someone throwing trash or broken appliances in a campfire.saddly human garbage gets everywhere these days. sciencemag.org/news/2014/06/… stick a red hot needle or pin in one of the smooth parts is should give off a recognizable buring plasitc smell. $\endgroup$ – John Sep 4 '18 at 3:22
  • $\begingroup$ Possibly some sort of clinker... Would fit to the luster and partly glass-like look $\endgroup$ – JulPal Sep 4 '18 at 22:21

Your rock is most likely some type of slag, typically from a metal foundry. Slag is commonly used in road and railroad construction and maintenance. Your rock may have been washed into the river by storm water.


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