It can be manufactured in a cement mixer. Why - I don't know. But you can. And here's the cost comparison:
[table=width: 500, class: grid, align: left]
[tr]
[td]Block name[/td]
[td]Raw material cost[/td]
[td]HP[/td]
[/tr]
[tr]
[td]Stone[/td]
[td]10 crushed sand, 22 small stone(4 in cement)[/td]
[td]500[/td]
[/tr]
[tr]
[td]Concrete Block[/td]
[td]10 crushed sand, 30 small stone(10 in cement)[/td]
[td]3000[/td]
[/tr]
[tr]
[td]Reinforced concrete Block[/td]
[td]Concrete way: 20 crushed sand,60 small stone(20 in cement)
Rebar frame way: 10 crushed sand, 30 small stone(10 in cement), 5 iron, 1/5 lump of clay[/td]
[td]9000[/td]
[/tr]
[/table]
Just going by material costs, effort put into and workstation needed for the block's creation, I would prolly agree that stone should have somewhat higher hp, close to that of first stage concrete. Or a more balanced recipe.