Keriscite

Keriscite in a crystal that forms around places of death and unrest, deep underground and within caverns. The crystal is created when stray necromantic energies seep into the rock, creating small slivers which resonate with similar energies. In its raw form, this mineral is jet-black and reminiscent of obsidian in its glass-like nature, with strands of dark purple within it. The stronger the necromantic energies that were present during its creation, the deeper the purple within. As a result, its value and strength is derived from the "violet grade".
Keriscite has had a long and troubled history, its existence considered evil and wrong by many of the devout. Most research into it has been done either in secret or under extreme supervision due to the dangers to society it poses. After a few uses were found, laws were passed to outlaw its trade and usage in common terms. However, the genie was out of the bottle so to speak, and black market traders are rarely known to carry this exceptionally valuable material. Even though usage and possession of keriscite is illegal in almost every large city, it has become nearly impossible to fully crack down on. A specialty of high-profile hitmen, the tell-tale purple scarring is known to be a dead giveaway to their handiwork with keriscite weaponry.
In its base form, it can be used as a focus and booster for necromantic magics. It appears to have some form of connection to the "soul", resonating with life in a way that isn't fully tested. Depending on its "violet grade", the weaponry it can be refined into is the main cause of its illegal nature. Very high-grade keriscite when killing a living creature can entrap their "soul" within the weapon and can often even consume the soul entirely, preventing resurrection through methods weaker than a Wish spell.