🔎 UNIDENTIFIED Native American Melted Rocks

[David_Swift]

Located these in a rock shelter with lots of flint laying on the surface. The smaller black rocks look like melted slag from melting metal but metal detector showed it was not metal. No home sites ever in this area. Just this and flint laying around. Any ideas?

 

[blauer]

It looks like burned up coal to me. What's the general hardness of it?

 

[David_Swift]

It looks like burned up coal to me. What's the general hardness of it?

That was my initial thought but the pieces are heavier than coal and they have smooth melted areas on the surface.