Emerald

Emeralds are one of the rarest materials in Minecraft.

Mining
Emerald ore mined using an iron or diamond pickaxe will drop one emerald. If the pickaxe is enchanted with fortune, it may drop an extra emerald per level of fortune, up to a maximum of 4 with Fortune III. If the ore is mined using a pickaxe enchanted with silk touch, it will drop itself.

Natural generation
Chests in Desert Temples and Jungle Temples may contain emeralds in stacks of 1 to 3. & in MCPE, in blacksmith chests.

Trading
Emeralds can be used for trading with villagers. Trading is a much easier and less time consuming way to obtain emeralds than mining is.