@Buri Is your server using mods that change recipes because if this is the case, then this is not part of the base game developed by Funcom but part of the mod created by the mod author. The vanilla base game recipe requires obsidian and steel.
EDIT: [Mod] Exiled land improved
• Obsidian weapons/tools : Now you need obsidian AND composite obsidian to craft obsidian stuff, BUT you need only obsidian to repair. In counterpart, composite recipe has changed (1 composite = 5 obsidians + 1 alchemical base + 1 steel fire).(modifié)