Reminds me of the
Gordon razor hone which I won. I showed it to Adrspach (Stepan) at the last UK razorcon and he told me he did not think it was a Yellow Lake, but another kind of slate. This has a very similar look and box. Mine looks little different after lapping. It closely resembles a BBW and has purple slurry. Has a few faint lines and a blue inclusion. A nice finisher, improves a Nani 8K and delivers a smooth shave.
EDIT: I went and had a look at my hone. It has the same very faint large streaks as yours.