From Lost Fables Wiki
Jet is one of the most common gemstones around. Being black and coarse naturally, it can be mistaken for coal in the dark of a mine, but immediately upon mining or touching it one would be able to discern the difference, as jet is significantly harder than coal. It is only rarely used in jewelry, being that it is not particularly valuable, and most of its uses for enchantment are in thieve's equipment and tools, making gear of any sort made of it relatively unlikely.
Generally speaking, when a gem is used for enchantments, it is either embedded into the metal of the weapon while it cools, or crushed into a fine powder and incorporated into the metal itself as it is forged.
Jet is mostly used for enchantments having to deal with darkness, either making things darker or harder to see, or gaining some form of increased power while in the shadows. For this reason, it is sometimes called the "Thieves' Stone."
Weaponry and Armor
Generally speaking, weaponry made with jet will grow more powerful or devastating while in darkness, while gear tends to grow more sturdy or allow the user to bring their own cloud of darkness around with them.
There are no jet Artifacts on Anoma, perhaps you can change this.