A great bournonite "cogwheel" from Yaogangxian-- in my opinion the bournonites from this mine are the best to come out in recent years. Bolivia certainly wins for quantity, but the pieces from there always seem to be lacking in at least one area, be it luster, size, or sharpness.
This is reasonably well sized for Yaogangxian, with good "cogwheel" faces on the sides and good luster. It does have a few chips, though nothing that particularly detracts, and the bottom is actually etched (not a contact!)
All in all, a great (and somewhat hard to obtain) example of bournonite from China-- far more complete than most!