For now it is an adventure hook with no specific use in terms of game mechanics.
Both the Starfinder Pact World's Campaign Guide (p 31) and the second Dead Suns adventure path module Temple of the Twelve (p 39) contain the same text:
In recent years... technomancers for the Astral Extractions mining company have discovered new magical uses for corpsicum, a rare material produced when water seeps through the kaymos’ cliffside burial grounds. The resulting influx of cash has let the corporation buy leaders and votes, and most of the city [Candares] is happy enough to let the crab-like mining robots scale their cliffs. Exasperated and unheeded, the Wallkeepers--traditionalist rebels from both races [lashunta and spider-limbed kaymos] who see the mining as a desecration of their ancestors--occasionally send the enormous machines falling in flames to the city below.
So corpsicum is an important commodity for the city of Candares and a reason for Astral Extractions' presence and seeking of influence in the city. It is also a cause for conflict between Astral Extractions/the majority of Candares' population and a minority militant group seeking to prevent the desecration of the kaymos burial ground in the cliffs. In short, it's an adventure hook for GMs to use if they want to run a campaign on Castrovel. It involves Astral Extractions--an established villainous entity from the Dead Suns adventure path--and a secret organization that creates dangerous situations in an urban setting. It also sets the stage for encounters with AE's crab-like mining robots and the Kaymo aliens who want the mining of corpsicum to stop.
The precise magical use of corpsicum is not given in either source, nor is it among the special materials described in the Starfinder Armory. This may change with future expansions; and of course any GM is free to define corpsicum's uses for his or her own campaign.