Defeating the four Vampire golems that animated as he descended into the chamber, Raziel was able to spawn several Earth platforms which allowed him to jump up to a higher ledge surrounding the room where he could discover the Obsidian Sphere on a similar stand.[Defiance][Defiance/10][Defiance strategy guide]
The item itself was a darkened sphere of black and orange/red material resembling volcanic rock.[Defiance][Defiance/10]
Although not identified in dialogue, the Obsidian Sphere is explicitly named as such in the inventory and its name is reiterated in the official guide. The Sphere is labelled in game files as "av_earthartifactkey" and its final holder is listed as "av_earthartifactlock".[Defiance][Defiance/10]
The 'Dark artifact' powered by the defeat of Shades
The Light associated 'Faceted Orb'
The 'Fire artifact' block powered by being set aflame
The Air associated 'Howling Heartstone'
The Earth associated 'Obsidian Sphere'
1/5
The name "Obsidian Sphere" suggests that the item is constructed or formed from Obsidian - a igneous rock formed in volcanoes from quickly cooled lava, which gives it a characteristic glassy appearance and black and red color.[1]
The Obsidian Sphere is one a number of related artifacts that are found in forge portal rooms and immediately used to access the portals. Other artifacts that are treated the same include the Faceted Orb for the Light Forge and the Howling Heartstone for the Air Forge.[Defiance][Defiance/4][Defiance/6][Defiance/10][Defiance strategy guide] Although not containing such 'keys', both the Dark and Fire forges have objects identified as "artifacts" in files that control portal activation, although they are not used in the same way the "key" artifacts are.[Defiance][Defiance/4][Defiance/6][Defiance strategy guide] Game files and textures reveal that the these 'artifacts' are similarly counted as an object rather than part of the room (although not as 'keys') and like the Faceted Orb they all have a subtle Darkness or Light symbols within their textures which are virtually invisible in the course of regular gameplay.[Defiance][Defiance/4]
Obsidian at Wikipedia
