Adamantine Obsidian

Adamantine obsidian is the near-unbreakable slippery black glass-like material from which the Thousand Towers are constructed. It is thought to have been created by fusing diamond with black iron.  It may be substituted as a spell component for a spell that requires a diamond.  A piece of adamantine obsidian is worth about ten times as much as a diamond of the same size, meaning a spell requiring 300 gp of diamond requires 3,000 gp worth of adamantine obsidian.   The last time that this material was produced was in the Third Cycle.  The secrets of its manufacture have been lost since the Great Sundering.   The remains of the Thousand Towers are made of this material. Other pieces, from tiny slivers to jagged lumps as big as a building, can be occasionally found buried beneath the earth across the surface of Casiphon, where they were thrown during the Great Sundering when the Thousand Towers were smashed to pieces along with the surface of the world.