DIAMOND

No villager on this site sells a diamond back to you, three of them buy it. An Armorer, a Toolsmith, and a Weaponsmith each open a diamond slot once they reach their own tier, all paying the same 1 emerald for 1 diamond, which makes a stray gem one of the more liquid things a player can carry into a trading hall.

What diamonds actually buy back is the interesting half. Chainmail and enchanted diamond gear, iron leggings, a bell: three separate shelves stacked with things a diamond eventually turns into once the emeralds it earned get spent somewhere else.

Three jobs, one identical rate. An Armorer pays 1 emerald for 1 diamond at journeyman, a Toolsmith the same at expert, and a Weaponsmith the same again at expert. None of the three quotes a better deal than the others, so which one buys first comes down to which villager reaches its tier first, not which trade is worth more.

No villager hands a diamond back to a player in exchange for emeralds. Every one of these three rows only runs the one way, out of your inventory and into theirs.

The best rate any villager offers is an emerald for a single diamond, from the Armorer, and nothing else on the list pays out faster. No villager sells diamond back, so it is emeralds out and nothing in.

One slot at the Armorer takes 1 diamond a trade, 12 trades, 12 emeralds. 8 of the 72 villagers that pay emeralds, emptied out:

12 acacia boats against 288 flint for the same 12 emeralds, 24 times the carrying, and the shortest wait is the Butcher at 7.5 real minutes of shelf, gathering not counted. Diamond itself pays 1 an emerald, so nothing in that table asks less and 62 ask more.

All three sellers gate diamond behind a mid-to-high tier rather than their opening shelf, so a freshly employed armorer, toolsmith, or weaponsmith needs several completed trades first before the offer even has a chance to show up in its pool.

Once open, each of the three slots sells 1 diamond at a time for 12 uses before locking, and a restock brings back the identical offer at the identical rate rather than rolling a new one.

12 diamonds close out one slot, and that villager needs 2 real minutes back at its workstation before the offer reopens. A Minecraft day runs 20 real minutes, room for exactly two of those refills.

One villager camped for a full day is worth 24 diamonds for 24 emeralds, the hard ceiling for that single workstation. Running all three professions at once during the same day multiplies that ceiling by three, since each job restocks on its own clock.

Build the hall with all three jobs if diamonds are the goal. A weaponsmith at expert already shows this trade every single time, so it is worth leveling one of those first if the choice is which workstation to prioritize.

Where they go back: chainmail boots is the cheapest thing that same Armorer sells you, for 1 emerald.

Also on the Armorer's list: enchanted diamond leggings, enchanted diamond boots, enchanted diamond helmet, enchanted diamond chestplate, coal, and iron leggings.

Villagers who buy diamonds pay well, but the emeralds rarely beat what the diamond does in your own hands: a pickaxe, a sword, or the enchanting setup that makes everything else last. Selling diamonds is usually a sign of having more than you can use.

They generate deep, they are the gate to obsidian and to the Nether, and they cannot be crafted from anything. Fortune on the pickaxe is the only real multiplier, and it applies before the villager ever sees them.

Diamonds generate deep, and deeper is better: the lowest levels of the world hold more of them than anywhere else, and a vein exposed to air generates less often than one buried in stone.

Beyond tools they are the enchanting table, the jukebox and the firework star's shape. The table is the one that matters: four obsidian, two diamonds and a book, and that obsidian needs a diamond pickaxe first.

Fortune multiplies what a vein gives, so the order of operations for a serious world is one pickaxe, one enchanting setup, then the mining that pays for everything else.