These Basalt rocks were hand cracked and used to build the walls on my home.

Many of these rocks have these semi circular pattern, made of the basalt itself. It's just a bit darker than the rest of the stone. I am wondering what caused it. Pattern on Basalt rock

  • 2
    $\begingroup$ Conchoidal fracture $\endgroup$
    – Siv
    Mar 11 at 17:10
  • $\begingroup$ likely a result of the tools used during the manufacturing process,a hydraulic hammer or a result from explosives used to fracture the rock.one can see two points of impact so probably from a hammer. $\endgroup$ Mar 11 at 19:22


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