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all the stones you have there are good for knives

hard arkansas is an oil stone its a middle of the road stone in a stone progression

the first stone is harder to identify the green on it i would assume its mold clean it up and your probably find a hard ark but i cant be sure until its clean

the mitteilein stone is man made probably silicon carbide the stone after that looks like slate

feel the back side of that two tone stone it looks to me to be a silicon carbide and a aluminum oxide is the black side ruff ?