"Clinker", regionally referred to as "scoria" is a pyrometamorphic rock that is commonly used as a surfacing material. These rocks are all samples of clinker- look at the amazing variety! Next: wtf is Pyrometamorphic?

"Pyrometamorphic" rocks, fo rmed through the process of pyrometamorphism (shocker, lol) are rocks that have been changed by the heat released from a fossil fuel fire such as a burning coal vein. These fires can be either natural or cause by humans (anthropogenic).

(Side note, sedimentary rocks trapped in volcanic lava may undergo pyrometamorphic tranformation.)

So! Clinker is derived from shale, siltstone, and sandstone beds that surrounding burned coal seams. (I'm not getting into the semantics of clinker vs buchites because I don't care. I call it scoria anyway). Look at the luster on those veins! So pretty!!!

True "scoria" looks very similar to the sample in the second picture in this thread, but instead of being pyrometamorphic it is an actual igneous rock.

But despite being a geo person, I call all of the clinker in my area Scoria. Because I'm not a fuckin narc