Fairly rough...but he did offer to clean it up. I declined as I wanted it shipped immediately. I got it about halfway flat in 15 minutes with a dry XXC DMT. The feel in lapping is similar to a slate, but with a quality I can only describe as 'ceramic'...though that isn't an assessment of the structure, just the feel. It abrades easily enough with the diamond plate...but that's relative to my expectations, not other siltstone/sandstone based materials. It's VERY hard. That said...it's got nothing on quartzite/chalcedony when it comes to difficulty flattening lol.