They are not all combos and even colour can vary. However as with this one my guess would be towards arkie.
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I agree having looked at the tables at Dan's honing site for Arkansas stones. The brown colored stones are in the "True Hard Arkansas grade" category are are extra fine grit at 1200+. Believe this stone is in that category as it is very hard and fine. This could be even finer. It needs to be lapped (I think) and will eventually end up a smaller stone. Getting there, thanks for your inputs/comments.
the second stone looks like a vintage hard ark
Just an informational note here. Be careful with boiling rocks. Rocks don't like quick drastic temperature changes. If there are any internal cracks and you boil for any length of time the rock can simply break into pieces.