Minecraft: Edition

I found a diamond in the tutorial in a chest in a house at X: -176, Y: 66, Z: Z: 124. Once out of the chest I had to drop it and pick it up a few times before the achievement unlocked.

UPDATE:
as per reply below from Tranierx:
Diamonds at X=-147 Y=97 Z=37 in Elytra Tutorial World

This achievement is very easy to get with the NEW TUTORIAL WORLD

First, skip through the tutorial and make your way to the beacon. Open the chest and grab the 5 pieces of iron. Chop down some trees to make some planks. Make a pickaxe with the planks by turning them into sticks, then head to the docks. Grab two boats and head under the bridge and keep going straight until you see the desert village. Walk past the village and place your second boat in the water. Then take a slight right and keep going till you see a huge pirate ship. There will be a building directly behind it. Sail around the front of the ship and make your way to a set of ladders.

Find a room called "the library and hit the lever to the left of the fire place. Walk through the fire place into a room. You will find a solid diamond block. Mine it with your pickaxe, then use a crafting table to convert it into 9 diamonds. Your achievement will hopefully pop then!

Also if you need The "Diamonds to you" Achievement. Simply grab an extra controller, sign in as a guest. Then throw a diamond () to the guest!

Happy hunting

Easiest way to get this in the latest version CU48 is to load up the tutorial world make your way to the beacon then turn left to the trading area turn right into the area with an anvil up the stairs to where the golem area is punch the tree to get wood grab an iron block convert the wood to sticks and the iron to iron ingots make a iron pickaxe then go up the stairs facing the bridge and yellow circle turn left and keep going until you get to the Elytra area there will be a block of diamond on a post mine that with the pickaxe then go back to the crafting table you walked past convert the diamond block into diamonds take them and the achievement will pop.

Diamonds are the best, and rarest, resource in the game. They are found deep inside of the world, often near lava. Find a piece of diamond, mine it and the achievement is yours!

Source:
https://www.xboxachievements.com/game/minecraft-xbox-one-edi...
All credit goes to the original writer.

Here's a video: