Round rocks, mineral or artifacts?

[erbridgehound]

I bought an entire rock collection. I have never seen these type of rocks before. They are not attracted to a magnet, so definitely not iron. They are a bit heavy. They are 1.5 inches and 1 inch in diameter. I get the sense when holding them that they could be hollow but not sure. They smell like rocks (earthy smell). What are these? Does anyone know? 

drive.google.com/file/d/11IPKDFYRbBqBRDIu_iXgOds2UpP3OgRY/view?usp=sharing

[victor1941]

They look like iron concretions.