Arcstones are bright blue, slightly glowing stones and valuable crafting ingredients that can mainly be obtained from Keepas of any kind.
How to obtain
When a wild Keepa of any kind is near, a symbol that resembles an Arcstone will start to blink and "pulsate" with blue circles on your compass on top of the screen.
Since update R47 on October 18th 2017 (Pumpkiru's Candy Campaign), Arcstones can now also randomly be obtained via Login Chests that can be claimed ca. every 4 hours for free. Please note that during event-times, the content of Login Chests might differ, will usually contain event-specific items, and Arcstones might temporarily become rarer.
While common blue Keepas usually only yield 1-5 Arcstones at a time either as a loot or pet-harvest, Silver Keepas can yield up to ca. 30 Arcstones, but only when killed, and Golden Keepas up to ca. 50 Arcstones also only when killed (perhaps rarely even more).
All types of Keepas can spawn literally everywhere, even on crafted blocks. But they spawn most often on the Corruption layer and in Caves underground, so you might want to hunt for them there for maximum efficiency.
Best take Corrupted Soup, Corrupted Sandwiches or Corrupted Pie with you that will turn Corruption damage into healing over time, if you go hunting Keepas on the Corruption layer. A few Healing Beacons and some ladders should also be very helpful. Ever since Creatures will now drop Loot Bags even if they die from drowning, freezing, burning, being poisoned or corrupted, Keepas might die from Corruption on the Corruption layer before you can catch them, but will still drop Arcstones.
If you tame either Silver Keepas or Golden Keepas, then feed them their favorite Food and later on harvest from them, you can usually only obtain 1-5 Arcstones with each harvest, different from their much richer loot that they will only drop when they are killed. You can receive the same amount of Arcstones from common blue Keepa-Pets too.
Please note that Pets will generally only provide you with their best harvest after you have fed them their exact favorite Food. You might not get any Arcstones from any type of Keepa otherwise. For example: if your Keepa Pet prefers Sandwiches (as shown in their pet window), but you feed them Turnip Sandwiches, its pet-harvest might only consist of Coal and Gunpowder, but no Arcstones.
How to use
Arcstones are required to craft Lumite Armguards, Lumite Breastplates, Lumite Leggings, Lumite Pauldrons, Lumite Swords, Arctek Chests, Grand Arctek Chests, Arctek Torches, Grand Arctek Torches, Arctek Lanterns, Grand Arctek Lanterns, Arctek Tables, Grand Arctek Tables, Delay Gates, Inverter Gates, Logic Gates, Number Comparison Gates, Galactic Flux Incapacitators, Block Phasers, Arc Signs, Small Capture Blocks, Medium Capture Blocks, Large Capture Blocks, Arc Picture Frames, Checkpoints, Adventure Gates, Sensors, Mob Spawners, Loot Spawners, Legendary Golden Swords, Rainbownator 5000s and the like.
Like many types of animal loot, Arcstones cannot be placed nor dragged into a quickslot nor directly into the world.
However, Arcstones are special in that they can be put on display in Wood Planters and Flower Pots, on Wall Shelves, Hidden Temple Altars and Placemats, as well as on Galactic Grav-Chambers, Snow Buried Containers, Frozen Containers and the like. They can glow a little in the night when on display, but without illuminating their surrounding.
In former versions of Creativerse, Arcstones could also be very rarely found in randomly spawning Wood Treasure Chests at night on the surface, but this is not the case any longer.