Thread: A Mystery Hone

Here's another I acquired recently but know little about. It's grey and feels very smooth, but not glossy. My fingernail can't make a mark on it. It's 4" long, 2" wide, and 7/8" thick.

I hope I'm not being a dufus to put up such an undistinguished rock and having the temerity to ask if anyone can ID it! I have, however, been astonished at the abilities of this community to do just that.