Post a photo of that JNat... a visible crack on the top doesn't sound good. If you can feel it with your fingertip, it will cause trouble when sharpening. A quality vendor will swap it out/replace it for you.

Wetting it down with water will help accentuate the crack for the photo (see mine attached, when I was working with a vendor). If you do decide to keep it, CA glue (superglue) followed by lapping can help save it... but again no reputable vendor should be selling a stone with a visible surface crack.

Cheers, HJ

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