It doesn't add up. I believe what you are saying but hard Ark and friable just doesn't go together. The really soft arks, some even carrying a Washita label are the only ones I have seen that could be described as friable. I think that stone is probably miss cast. It doesn't make the stone any less useful though.vintage washita 427gm 2x6x1
white hard ark 491gm 2x8x1
the vintage washita feels much denser
white hard ark is porous and friable compared vintage washita