I work with granite a fair amount and pick it up at a Concord quarry on occasion, the one you can see (look for the derricks) off on a rise to the east of the city from I93

They slab huge blocks into thinner pieces with a giant circ saw, maybe a 14' blade, it makes multiple shallow water cooled cuts, guessing it might be taking a 1/4" per pass, dropping down into the block hour upon hour, day in day out. Multiple automated saws in multiple sheds cutting with little or no human supervision.

Guessing again, that the pictured piece was cut in that fashion and somewhere in the process the saw broke down and left those mill marks ???

I see lots of granite in both house and barn foundations, and though this is only an observation, quarried granite becomes less frequent the father you get from the quarries. It disappears from barn except for maybe piers in manure bays, and is used only on the street side in house foundations. I believe this probably had to do with the expense of transport which must have been charged by the mile.