The Crystal of Air is a silver fragment with the Kryptonian symbol for "Air", and "S".
Powers and Abilities
It is unknown if the Crystal of Air possessed any powers by itself. While Clark Kent and Countess Margaret Isobel Thoreaux (who was possessing Lana Lang) were fighting, both of them touched the crystal, which blasted both of them and caused Lana to regain control of her body.
When combined with the Crystal of Fire, the Crystal of Air was capable of revealing the location of the Crystal of Water with a Kryptonian beacon. When combined with the other two Stones of Power, the combined crystals became the Crystal of Knowledge. (Commencement)
In 2005, the Crystal of Air was discovered using an ancient manuscript purchased by Lex Luthor, who eventually learned that the manuscript contained a hidden map. Along with Jason Teague, Lex traveled to a temple in Shanghai, but he and Jason were taken into custody and tortured by Chinese officers. When Clark and Lana followed them to Shanghai, Lana was captured and tortured as well, causing Isobel to possess her once again. Isobel incapacitated Clark long enough to find the Crystal of Air. Clark battled Isobel, but in the process, they lost track of the Crystal of Air; Jason was able to pocket it unnoticed and mail it to himself from Shanghai to Smallville where he showed Lana he had it. Later, Lana staged a break-in at their apartment above the Talon, leading Jason to believe that Lionel Luthor had stolen the Crystal of Air.
Later, Jason and his mother Genevieve Teague kidnapped Lex and Lionel, and tortured them to get back the Crystal of Water that Lionel stole from them. Lionel lied and told them that he gave it to Lana, so Genevieve confronted Lana and demanded the stone. They struggled, and when Genevieve began to strangle Lana, Isobel emerged once more and used the Crystal of Air to stab Genevieve in the chest, killing her. Because she had stained the crystal with human blood, Isobel retreated and the Mark of Transference disappeared from Lana's back.
However, because the Crystal of Air was stained with human blood, another meteor shower headed toward Earth, particularly Smallville. (Presumably, the blood on the crystal "activated" it as a beacon to other Kryptonian artifacts, waking the Black Ship and the Disciples of Zod, sending it from high orbit to a rendezvous trajectory.)
Lana entrusted the "murder weapon" to Clark for safekeeping, and Clark took the Crystal of Air to the Kawatche Caves where he united it with the Crystal of Fire. Once united, the two crystals revealed to Clark the location of the Crystal of Water.
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