|Map||Basic Data||Planetary Image|
|Class:||Adeptus Astartes Homeworld|
Obsidia was formerly the homeworld of the Astral Knights chapter, before their near-complete annihilation in the battle with the Necron World Engine; afterwards, the High Lords of Terra ceded the Knights' fortress-monastery and chapter possessions to the Sable Swords.
Later, the bulk of the Sable Swords fought against Eldar on Larical's Folly. This left Obsidia vulnerable to an attack by the mutant horde of the Twisted Convocation. Obsidia was rescued by the intervention of the Novamarines, prompting the Sable Swords to swear an oath of eternal debt to their saviours.