Ebonstone

Ebonstone is a rare mineral hidden deep within the crevices of the Gloomdepths. It's dark, iridescent gleam and otherworldly luminescence swirling in its eternal depth display the arcane power it harbors within. This stone is more than just a magical anomoly, it is the cornerstone of the forbidden arts and operations of The Obsidian Syndicate.
In its raw state, Ebonstone pulsates from within a swirling mass of primal energy. Its mystical might can be awoken when it is pulverized into a fine, shimmering powder. The powder forms the basis of the Syndicate's rituals, its mysterious energy being the key component in their Shadow magic.
The Ebonstone powder is also reformed into various shaped crystals that allow its power to be defined by the crystalline structure given to it, especially when magical glyphs are etched into it. The powder can also be used for more permanent Shadowscript markings, where the magical properties allow it to sink into any surface becoming undetectable without the use of the Syndicate's detection spells.
The collection of Ebonstone is no easy feat, it is guarded by a myriad of particularly nasty creatures. There are even rumors that if too much Ebonstone is harvested, the Ebonstone dragon will awaken and set Seiderheim into another age of ice. The Syndicate has a ritualistic process to collect the Ebonstone and always offers gifts signifying praise and thanks to the Ebonstone Dragon, never taking more than they need.
Once the Ebonstone is harvested it must be carefully transported, it is a volatile material and the occasional accident results in many deaths. They often say that the deaths are caused by ignoring the might of the Ebonstone Dragon and offer a reminder to always respect the Ebonstone.
In the Cavern of Shadows lies the largest Ebonstone crystal, shielding the whole obsidian spire from certain magics.