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Black hard Arks & translucent Arks are more like finishers but you won't know till you try it.
Coarse water based valve grinding paste on flat glass is quite effective for lapping Arks but messy.

I'd bet its a combo hone , Ali ox on one side Ark on the other. Probably a knife hone but try the Ark it may be useful but not likely a finisher. & yes lap it flat.