In vanilla Minecraft, you can make armor out of all BUT which of the following?

In vanilla Minecraft, you can make armor out of various materials such as iron, gold, and diamond, as they are commonly found resources within the game. However, Emeralds cannot be used in crafting armor. Though Emeralds are valuable in trading with villagers and as a currency in the game, they are not recognized as a material that can be utilized to create armor. Therefore, Emeralds stand as the exception among the listed options for crafting armor in vanilla Minecraft.