As you wander around the world in Nexomon: Extinction you will come across stones filled with multicolored gems. You can crack these stones to harvest the gems as long as you have a pickaxe. Thankfully, you can grab a pickaxe quite early in the game, and you should definitely get it as quickly as you can from the NPC near the Orphanage. This will allow you to farm up Shards as soon as you start playing the game, and you are going to need a lot of them.
You can use shards to trade-in at the General Store for Gold, as a means to get items from certain wandering traders, and you can use them to synthesize Cores. Cores are very useful items you can equip on your Nexomon to improve their base stats.
Cores are definitely the most important use of Shards, so make sure you are selling ones that you don’t need to improve your Nexomon. Truthfully, Gold is not difficult to come by in the game, so you have no reason not to hold on to your shards for synthesis and merchant trades.
How to Synthesis Cores
You can synthesis Cores once you get to Parum. To get to the building you need to be into synthesis cores, go directly left from the Parum warpstone until you leave the screen. Cross the bridge and then go north. You will come to a large fountain with an ornate building directly behind it. This is where you need to go.
In the back of the building, you can find Bonnie and the Synthesis Machine. Here, you can choose from a rank of Cores, at different ranks, and use your Shards to creat them. Each core requires a different amount of shards, of varying types, for you to be able to Synthesis it.