Minecraft wiki entry for Unused_textures, associated text: Doors were ultimately added on the 7th of June, 2010, as a relatively normal block, which would instantly open or close when interacted with, having no continuous animation in the process as had been mentioned. However, the /item directory in minecraft.jar, which stored the textures for other non-mob entities at that time such as minecarts and arrows, gained a texture called door.png in this same version, which is without a doubt linked to said opening/closing animation. An early iteration of the oak door can be seen in it, with empty space filled out in solid purple in a fashion resembling the placeholder texture from terrain.png and kz.png as well as the checkerboard missing texture.