I have seen rock being used as decorative bricks and those folks would use a copper saw with some sand to make the gouge, lodge a chisel in the gouge and smartly tap it with. Once every bit was tapped - one strike would slice the brick shaped rock.

This was in the ME - but may work for your bricks too.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)