Minecraft wiki entry for Seamless_Stone_Slab, associated text: The seamless stone slab can be visually distinguished from normal smooth stone slabs via the texture they use: while smooth stone slabs have a dedicated side texture as to make single slabs appear polished, and double slabs appear to be composed of two single slabs, the seamless stone slab's side texture appears cut off in single form, and in double form identical to smooth stone. Indeed, the seamless stone double slab was itself a precursor to smooth stone, which would end up being implemented intentionally.