Cousin in Arkansas found it. No additional info.
From the picture, it just looks like a chunk of basalt with some lichen growing on it, but I’m not sure if that makes sense anywhere in Arkansas where there’s very few igneous rocks and pretty much no volcanic ones*. It looks like there’s some dark-colored intrusive igneous rocks in some very small parts of the state, most famously in the diamond-producing localities, so my guess would be something like peridotite or kimberlite.
(*Except in the Coen Brothers’ version of it. Their version of True Grit, which is supposed to take place in western Arkansas and eastern Oklahoma rather prominently features the basalt flows in New Mexico where much of it was filmed. Still better than the Sierra Nevadas and Colorado Rockies in the '69 version.)
I was going to guess some clastic igneous rock like peridotite as well. Is there really none of this among the synclines and anticlines of the Ouachita Mountains (often lumped in with the Ozarks)?
Too far south for glacial erratics, of course.
From that photo, it would be absolutely impossible to do anything but guess. Looks fine-grained and dark, overall. Can’t tell if the white bits are part of the rock or just adhering to it. Could be anything from fine-grained igneous rock - lava or glass - to mudstone, to chert. Given the little I know about Arkansas stratigraphy, I’m going to go with chert.
But definitely not peridotite or kimberlite. Both are coarse-grained (kimberlite being often distinctly phenocrystic), and often noticeably green.
And people, learn to put a scale in your photos.
If it makes any difference, northwestern Arkansas.
Perhaps it is the little rock they named their state capital after. 
I should add that the reason I say chert rather than some of the other choices is because I’m seeing some traces of conchoidal fracture, but not as marked as I’d expect from actual glass like obsidian.
yeah, I’m going with chert. Possibly metamorphosed to novaculite, but I think that’s the wrong part of the state for that.
Yeah, I was thinking for it to be peridotite or kimberlite it was a somewhat blurry photo and/or a small actual rock with similar-colored minerals, but I’ll bet chert is absolutely right.
Thanks, all.
No problem.
For future reference, it’s a little easier to do rock ID if
a) there’s something in the photo for scale (a pen, a coin, a lens cap)
b) the rock is washed down first.
Did he find it on some cyclopean stonework with non-Euclidean geometry? Odd piping noises? Has he been having odd nitemares?
Nah, some French guy swiped it.
There is a volcanic uplift, if I use the right term near LR close to the junction of I-430 and I-630. A house sized piece or rock was pushed up and the horizontal layers turned up and down uppity million years ago.
The UALR geology teacher takes students to see it.
I found it on Google Map.
Am I a geek, or what?
Looks like possibly a dyke in that road cutting, hard to say just from Street View. But that’s an intrusive and wouldn’t be anywhere near as fine-grained as the OP’s rock. There aren’t any volcanic rocks anywhere near Little Rock - the closest igneous outcrop is somenepheline syeniteto the south. Which looks nothing like glass or chert.
And in researching that, I found this amazing website put out by the USGS. You can zoom, click on any unit and get the basic info on what stratigraphic unit and rock types are there - amazing!