I was playing in Silver Knight Gate, Wasteworks - Infernal Passage (Depth 19) with my friend (looking for Punkin King) and we came upon this Mineral deposit without part of its' side.

http://steamcommunity.com/sharedfiles/filedetails/?id=103285919

This is a minor bug, and maybe the model for it was used when they are against a wall? I would suggest just using the 4 sided version for all mineral spawns.