Minecraft wiki entry for Unused_textures, associated text: Alongside emeralds, 12w21a also implemented emerald ore as a method of obtaining them. However, the intended emerald ore was accidentally left out of this release,[20] and as such the emerald ore block instead used a texture clearly more reminiscent of something that would yield rubies as a drop. Java Edition 12w21b was swiftly released to patch this, giving emerald ore its intended release texture. There were also translation strings in the game's language files referencing rubies and ruby ore, which were ultimately removed in the full release of Java Edition 1.10: