That looks like a concrete block to me. Cinder blocks are an inferior product and I'm not sure they are made in the states anymore. Cider blocks are much more porous
Cinders, slag from smelters were formed into blocks and used as cheap building material,they were about 30% lighter in weight and had much less compression strength. They were mainly used for small buildings. The residuals in the material probably helped shut down the use of these things, lead, zinc etc.