There appears to be a misunderstanding in this thread.
The xenomorphs are not silicon-based.
In Alien, Ash (the android) notes that the facehugger utilizes utilize silicon-based processes to replace its outer layer...he specifically calls out the "interesting combination of elements". [1] It wouldn't be necessary to call out the use of silicon for the outer layer if the entire organism was silicon-based.
Also, it's clear that the xenomorphs utilize carbon-based food to grow baby xenos. In Alien, the host complains of starving before the baby pops out of his chest. Moreover, humans lack sufficient quantities of silicon for a baby xeno to grow in a human. In David's lab (Alien: Covenant), David's notes and experiments also indicate a duality to the creatures, and also that they are not strictly organic lifeforms, but are a fusion of organic and non-organic life...which is part of his fascination with them.
[1] In the novelization of Alien, Ash goes even further, stating that they facehugger is both carbon-based and silicon-based.
The xenomorphs are not silicon-based.
In Alien, Ash (the android) notes that the facehugger utilizes utilize silicon-based processes to replace its outer layer...he specifically calls out the "interesting combination of elements". [1] It wouldn't be necessary to call out the use of silicon for the outer layer if the entire organism was silicon-based.
Also, it's clear that the xenomorphs utilize carbon-based food to grow baby xenos. In Alien, the host complains of starving before the baby pops out of his chest. Moreover, humans lack sufficient quantities of silicon for a baby xeno to grow in a human. In David's lab (Alien: Covenant), David's notes and experiments also indicate a duality to the creatures, and also that they are not strictly organic lifeforms, but are a fusion of organic and non-organic life...which is part of his fascination with them.
[1] In the novelization of Alien, Ash goes even further, stating that they facehugger is both carbon-based and silicon-based.