Doors and hatches
Fake Cabinet Door 1x1 Concrete
Zombies can see through this block. The intended use is that a hidden zombie can see the player and bust out of a closet.
Harvest drops
Small Stone× 25
Taken apart with a harvesting tool (axe, pickaxe, shovel), before perks and tool bonuses.
When it collapses
Falling, it leaves 
Destroyed Stone (75% of the time) where it lands.
Where to find (5 POIs)
Haven Hotel (tier 5), Vanity Tower (tier 5), Installation Blue Ridge (tier 4), The Señor Drogas Residence (tier 3), Mortabury Cemetery.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.